Force-measuring and touch-sensing integrated circuit device

ABSTRACT

A force-measuring and touch-sensing integrated circuit device includes a semiconductor substrate, a thin-film piezoelectric stack overlying the semiconductor substrate, piezoelectric micromechanical force-measuring elements (PMFEs), and piezoelectric micromechanical ultrasonic transducers (PMUTs). The thin-film piezoelectric stack includes a piezoelectric layer. The PMFEs and PMUTs are located at respective lateral positions along the thin-film piezoelectric stack, such that each of the PMFEs and PMUTs includes a respective portion of the thin-film piezoelectric stack. Each PMUT has a cavity, the respective portion of the thin-film piezoelectric stack, and first and second PMUT electrodes. Each PMFE has the respective portion of the thin-film piezoelectric stack, and first and second PMFE electrodes. Each PMFE is configured to output voltage signals between the PMFE electrodes in accordance with a time-varying strain at the respective portion of the piezoelectric layer resulting from a low-frequency mechanical deformation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 62/947,748 filed on Dec. 13, 2019, entitledFORCE-MEASURING AND TOUCH-SENSING INTEGRATED CIRCUIT DEVICE, and U.S.Provisional Patent Application No. 63/048,914 filed on Jul. 7, 2020,entitled FORCE-MEASURING AND TOUCH-SENSING INTEGRATED

CIRCUIT DEVICE, which are incorporated herein by reference in theirentireties.

BACKGROUND

The fabrication of piezoelectric micromechanical ultrasonic transducers(PMUTs) can be integrated with CMOS semiconductor processing. PMUTs canbe fabricated by MEMS processing and include a piezoelectric layer in apiezoelectric capacitor configuration, including one electrode on oneside of the piezoelectric layer and another electrode on another side ofthe piezoelectric layer. For example, a PMUT can be configured as atransmitter (ultrasonic transmitter) or a receiver (ultrasonicreceiver). The resulting integrated circuit can be a touch-sensingintegrated circuit and can include a semiconductor substrate (typically,a silicon substrate), signal processing circuitry on the semiconductorsubstrate, and one or more PMUTs overlying the semiconductor substrate.A high level of integration can be achieved by connecting the PMUTelectrodes to the signal processing circuitry on the semiconductorsubstrate.

In some use cases, the aforementioned touch-sensing integrated circuitis processed into an integrated circuit package. The IC packagetypically contains an epoxy adhesive on top of the PMUT. The IC packageis combined with a cover layer having an exposed outer surface and aninner surface, the IC package being attached to the inner surface viaanother adhesive. In such use cases, the touch-sensing integratedcircuit can be used to detect touching of the exposed outer surface by adigit, such as a human finger. However, in order to obtain betterfunctionality and discrimination, an integrated circuit device capableof concurrently detecting touch and measuring an applied force isdesired.

SUMMARY OF THE INVENTION

In one aspect, a force-measuring and touch-sensing integrated circuitdevice includes a semiconductor substrate, a thin-film piezoelectricstack overlying the semiconductor substrate, piezoelectricmicromechanical force-measuring elements (PMFEs), and piezoelectricmicromechanical ultrasonic transducers (PMUTs). The thin-filmpiezoelectric stack includes a piezoelectric layer. The PMFEs and PMUTsare located at respective lateral positions along the thin-filmpiezoelectric stack, such that each of the PMFEs and PMUTs includes arespective portion of the thin-film piezoelectric stack.

In another aspect, each PMUT has: (1) a cavity, (2) the respectiveportion of the thin-film piezoelectric stack, (3) a first PMUT electrodeon one side of the thin-film piezoelectric stack, and (4) a second PMUTelectrode on another side of the thin-film piezoelectric stack. Thecavity is positioned between the thin-film piezoelectric stack and thesemiconductor substrate. The PMUTs include transmitters and receivers.The transmitters are configured to transmit, upon application of voltagesignals between the respective PMUT electrodes, ultrasound signals inlongitudinal mode(s) along a normal direction approximately normal tothe piezoelectric layer and away from the cavities. The receivers areconfigured to output, in response to ultrasound signals arriving alongthe normal direction, voltage signals between the respective PMUTelectrodes.

In yet another aspect, each PMFE has: (1) the respective portion of thethin-film piezoelectric stack, (2) a first PMFE electrode on one side ofthe thin-film piezoelectric stack, and (3) a second PMFE electrode onanother side of the thin-film piezoelectric stack. Each PMFE 15configured to output voltage signals between the PMFE electrodes inaccordance with a time-varying strain at the respective portion of thepiezoelectric layer resulting from a low-frequency mechanicaldeformation.

The above summary of the present invention is not intended to describeeach disclosed embodiment or every implementation of the presentinvention. The description that follows more particularly exemplifiesillustrative embodiments. In several places throughout the application,guidance is provided through examples, which examples can be used invarious combinations. In each instance of a list, the recited listserves only as a representative group and should not be interpreted asan exclusive list.

BRIEF DESCRIPTION OF THE FIGURES

The disclosure may be more completely understood in consideration of thefollowing detailed description of various embodiments of the disclosurein connection with the accompanying drawings, in which:

FIG. 1 is a schematic view of an illustrative apparatus including atleast one force-measuring, touch-sensing integrated circuit device.

FIG. 2 is a schematic cross-sectional view of a force-measuring,touch-sensing integrated circuit device.

FIG. 3 is a schematic cross-sectional view of a certain portion of theforce-measuring, touch-sensing integrated circuit device of FIG. 2.

FIG. 4 is a schematic cross-sectional view of a deformable portion of athin-film piezoelectric stack.

FIGS. 5, 6, and 7 are schematic cross-sectional views of a PMUTtransmitter.

FIGS. 8, 9, and 10 are schematic cross-sectional views of a PMUTreceiver.

FIG. 11 is a schematic cross-sectional view of a piezoelectricmicromechanical force-measuring element (PMFE).

FIGS. 12, 13, and 14 are schematic side views of a force-measuring,touch-sensing integrated circuit device and a cover layer, attached toeach other and undergoing deformation.

FIGS. 15, 16, and 17 are schematic top views of the MEMS portions offorce-measuring, touch-sensing integrated circuit devices.

FIGS. 18, 19, 20, 21, and 22 are schematic top views of PMUT arrays.

FIG. 23 is a flow diagram of a process of making an integrated circuitdevice and an apparatus according to the present invention.

FIG. 24 is an electronics block diagram of a force-measuring,touch-sensing integrated circuit device according to the presentinvention.

FIG. 25 is a schematic cross-sectional view of a set (pair) ofpiezoelectric micromechanical force-measuring elements (PMFEs).

FIG. 26 is a block diagram illustrating the electrical connections ofthe PMFE pair of FIG. 25 to related signal processing circuitry in anintegrated circuit device according to the present invention.

FIG. 27 is a block diagram illustrating the electrical connections of aset of PMFEs to related signal processing circuitry in an integratedcircuit device according to the present invention.

FIG. 28 is a schematic top view of a PMUT showing an outer electrode andrelease holes.

FIG. 29 is a block diagram illustrating the electrical connections ofthe PMUT of FIG. 26 to related signal processing circuitry in anintegrated circuit device according to the present invention.

FIGS. 30, 31, 32, 33, and 34 are block diagrams of differentimplementations of force-measuring, touch-sensing integrated circuitdevices and associated circuitry.

FIG. 35 is a diagram showing a graphical plot of example PMUT digitaldata over a longer time duration.

FIG. 36 is a diagram showing graphical plots of example PMUT digitaldata over a shorter time duration.

FIGS. 37 and 38 are diagrams showing graphical plots of PMUT digitaldata and PMFE digital data, respectively, in response to an exampletouch event.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present disclosure relates to force-measuring and touch-sensingintegrated circuit devices and apparatuses incorporating them.

In this disclosure:

The words “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful and is not intended to exclude other embodiments from the scopeof the invention.

The terms “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

Unless otherwise specified, “a,” “an,” “the,” and “at least one” areused interchangeably and mean one or more than one.

The recitations of numerical ranges by endpoints include all numberssubsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, 5, etc.).

For any method disclosed herein that includes discrete steps, the stepsmay be conducted in any feasible order. As appropriate, any combinationof two or more steps may be conducted simultaneously.

FIG. 1 is a schematic view of an apparatus 100 according to the presentinvention. In the example shown, apparatus 100 includes force-measuringand touch-sensing integrated circuit (FMTSIC) devices 102, 106. Wesometimes refer to an FMTSIC device as an FMTSIC. In other examples, itis possible for an apparatus to have a single integrated circuit deviceor more than two integrated circuit devices. Each of the FMTSIC devices102, 106 has an electrical interconnection surface (bottom surface) 101,105 and an ultrasound transmission surface (top surface) 103, 107. Inthe example shown, each FMTSIC device 102, 106 is in the form of asemiconductor die in a package. The FMTSIC devices are mounted to aflexible circuit substrate 108 (e.g., an FPC or flexible printedcircuit) on the electrical interconnection surfaces 101, 105. Theflexible circuit substrate 108 is electrically and mechanicallyconnected to a printed circuit board (PCB) 112 via a connector 116.Other ICs 114 are mounted on the PCB 112, and such other ICs 114 couldbe a microcontroller (MCU), microprocessor (MPU), and/or a digitalsignal processor (DSP), for example. These other ICs 114 could be usedto run programs and algorithms to analyze and categorize touch eventsbased on data received from the FMTSIC devices 102, 106.

Apparatus 100 includes a cover layer 120 having an exposed outer surface124 and an inner surface 122. The cover layer 120 could be of any robustlayer(s) that transmits ultrasound waves, such as wood, glass, metal,plastic, leather, fabric, and ceramic. The cover layer should be robustbut should be sufficiently deformable, such that a deformation of thecover layer is transmitted to the PMFEs in the FMTSIC devices, asdescribed in FIGS. 12, 13, and 14. The cover layer 120 could also be acomposite stack of any of the foregoing materials. The FMTSIC devices102, 106 are adhered to or attached to the inner surface 122 of thecover layer 120 by a layer of adhesive 110. The choice of adhesive 110is not particularly limited as long as the FMTSIC remains attached tothe cover layer. The adhesive 110 could be double-sided tape, pressuresensitive adhesive (PSA), epoxy adhesive, or acrylic adhesive, forexample. FMTSIC devices 102, 106 are coupled to the inner surface 122.In operation, the FMTSIC devices 102, 106 generate ultrasound waves inlongitudinal modes that propagate along a normal direction 190, shown inFIG. 1 as being approximately normal to the exposed outer surface 124and the inner surface 122 of the cover layer. Stated more precisely, thenormal direction 190 is normal to a piezoelectric layer. Since thepiezoelectric layer defines a plane of a piezoelectric capacitor, thenormal direction 190 is approximately normal to a plane of thepiezoelectric capacitor. The generated ultrasound waves exit the FMTSICdevices 102, 106 through the respective ultrasound transmission surfaces103, 107, through the adhesive layer 110, then through the inner surface122, and then through the cover layer 120. The ultrasound waves reach asense region 126 of the exposed outer surface 124. The sense region 126is a region of the exposed outer surface 124 that overlaps the FMTSICdevices 102, 106.

FIG. 1 illustrates a use case in which a human finger 118 is touchingthe cover layer at the sense region 126. If there is no object touchingthe sense region 126, the ultrasound waves that have propagated throughthe cover layer 120 are reflected at the exposed outer surface (at theair-material interface) and the remaining echo ultrasound waves travelback toward the FMTSIC devices 102, 106. On the other hand, if there isa finger 118 touching the sense region, there is relatively largeattenuation of the ultrasound waves by absorption through the finger. Asa result, it is possible to detect a touch event by measuring therelative intensity or energy of the echo ultrasound waves that reach theFMTSIC devices 102, 106.

It is possible to distinguish between a finger touching the sense region126 and a water droplet landing on the sense region 126, for example.When a finger touches the sense region 126, the finger would also exerta force on the cover layer 120. The force exerted by the finger on thecover layer can be detected and measured using the PMFEs in the FMTSIC.On the other hand, when a water droplet lands on the sense region, theforce exerted by the water droplet on the PMFEs would be quite small,and likely less than a noise threshold. More generally, it is possibleto distinguish between a digit that touches and presses the sense region126 and an inanimate object that comes into contact with the senseregion 126. In both cases (finger touching the sense region or waterdroplet landing on the sense region), there would be a noticeabledecrease in an amplitude of the PMUT receiver signal, indicating a touchat the sense region, but there might not be enough information from thePMUT receiver signal to distinguish between a finger and a waterdroplet.

There are numerous possible embodiments of the apparatus 100. Forexample, the FMTSICs can replace conventional buttons on Smartphones,keys on computer keyboards, sliders, or track pads. The interiorcontents 128 of apparatus 100 (e.g., FMTSICs 102, 106, flexible circuitsubstrate 108, connector 116, PCB 112, other ICs 114) can be sealed offfrom the exterior 123 of the cover layer 120, so that liquids on theexterior 123 cannot penetrate into the interior 121 of the apparatus100. The ability to seal the interior of the apparatus from the outsidehelps to make an apparatus, such as a Smartphone or laptop computer,waterproof. There are some applications, such as medical applications,where waterproof buttons and keyboards are strongly desired. Apparatus100 can be a mobile appliance (e.g., Smartphone, tablet computer, laptopcomputer), a household appliance (e.g., washing machine, dryer, lightswitches, air conditioner, refrigerator, oven, remote controllerdevices), a medical appliance, an industrial appliance, an officeappliance, an automobile, or an airplane, for example.

The force-measuring, touch-sensing integrated circuit (FMTSIC) device isshown in greater detail in FIG. 2. FIG. 2 is a cross-sectional view theFMTSIC device 20, which is analogous to devices 102, 106 in FIG. 1.FMTSIC device 20 is shown encased in a package 22, with an ultrasoundtransmission surface (top surface) 26 and electrical interconnectionsurface (bottom surface) 24. Ultrasound transmission surface 26 isanalogous to surfaces 103, 107 in FIG. 1 and electrical interconnectionsurface 24 is analogous to surfaces 101, 105 in FIG. 1. The FMTSICdevice 20 includes a package substrate 30, semiconductor portion (chip)28 mounted to the package substrate 30, and an encapsulating adhesive32, such as an epoxy adhesive. After the semiconductor die 28 is mountedto the package substrate 30, wire bond connections 38 are formed betweenthe die 28 and the package substrate 30. Then the entire assemblyincluding the die 28 and the package substrate 30 are molded(encapsulated) in an epoxy adhesive 32. The epoxy side (top surface orultrasound transmission surface 26) of the FMTSIC device is adhered to(coupled to) the inner surface 122 of the cover layer 120. The FMTSICdevice 20 is shown mounted to the flexible circuit substrate 108. It ispreferable that the FMTSIC device have lateral dimensions no greaterthan 10 mm by 10 mm. The wire bond connection is formed between the topsurface 36 of the semiconductor die 28 and the package substrate 30.Alternatively, electrical interconnections can be formed between thebottom surface 34 of the semiconductor die 28 and the package substrate.The semiconductor die 28 consists of an application-specific integratedcircuit (ASIC) portion and a micro-electro-mechanical systems (MEMS)portion. A selected portion 130 of the semiconductor die 28 is shown incross-section in FIG. 3.

FIG. 3 is a schematic cross-sectional view of a portion 130 of theforce-measuring, touch-sensing integrated circuit device of FIG. 2. Thesemiconductor die 28 includes a MEMS portion 134 and an ASIC portion136. Between the ASIC portion 136 and the MEMS portion 134, the MEMSportion 134 is closer to the ultrasound transmission surface 26 and theASIC portion 136 is closer to the electrical interconnection surface 24.The ASIC portion 136 consists of a semiconductor substrate 150 andsignal processing circuitry 137 thereon. Typically, the semiconductorsubstrate is a silicon substrate, but other semiconductor substratessuch as silicon-on-insulator (SOI) substrates can also be used.

The MEMS portion 134 includes a PMUT transmitter 142, a PMUT receiver144, and a PMFE 146. The MEMS portion 134 includes a thin-filmpiezoelectric stack 162 overlying the semiconductor substrate 150. Thethin-film piezoelectric stack 162 includes a piezoelectric layer 160,which is a layer exhibiting the piezoelectric effect. Suitable materialsfor the piezoelectric layer 160 are aluminum nitride, scandium-dopedaluminum nitride, polyvinylidene fluoride (PVDF), lead zirconatetitanate (PZT), K_(x)Na_(1−x)NbO₃ (KNN), quartz, zinc oxide, and lithiumniobate, for example. For example, the piezoelectric layer is a layer ofaluminum nitride having a thickness of approximately 1 μm. Thepiezoelectric layer 160 has a top major surface 166 and a bottom majorsurface 164 opposite the top major surface 166. In the example shown,the thin-film piezoelectric stack 162 additionally includes a topmechanical layer 156, attached to or adjacent to (coupled to) top majorsurface 166, and a bottom mechanical layer 154, attached to or adjacentto (coupled to) bottom major surface 164. In the example shown, thethickness of the top mechanical layer 156 is greater than the thicknessof the bottom mechanical layer 154. In other examples, the thickness ofthe top mechanical layer 156 can be smaller than the thickness of thebottom mechanical layer 154. Suitable materials for the mechanicallayer(s) are silicon, silicon oxide, silicon nitride, and aluminumnitride, for example. Suitable materials for the mechanical layer(s) canalso be a material that is included in the piezoelectric layer 160,which in this case is aluminum nitride. In the example shown, the topmechanical layer and the bottom mechanical layer contain the samematerial. In other examples, the top mechanical layer and the bottommechanical layer are of different materials. In other examples, one ofthe top mechanical layer and the bottom mechanical layer can be omitted.When coupled to the cover layer, the FMTSIC device 20 is preferablyoriented such that the piezoelectric layer 160 faces toward the coverlayer 120. For example, the FMTSIC device 20 is oriented such that thepiezoelectric layer 160 and the cover layer 120 are approximatelyparallel.

For ease of discussion, only one of each of the PMUT transmitters, PMUTreceivers, and PMFEs is shown in FIG. 3. However, a typical FMTSIC cancontain a plurality of PMUT transmitters, PMUT receivers, and PMFEs. ThePMUT transmitters, the PMUT receivers, and the PMFEs are located alongrespective lateral positions along the thin-film piezoelectric stack162. Each PMUT transmitter, PMUT receiver, and PMFE includes arespective portion of the thin-film piezoelectric stack.

Each of the PMUTs is configured as a transmitter (142) or a receiver(144). Each PMUT (142, 144) includes a cavity (192, 194) and arespective portion of the thin-film piezoelectric stack 162 overlyingthe cavity (192, 194). The cavities are laterally bounded by an anchorlayer 152 which supports the thin-film piezoelectric stack. Suitablematerials for the anchor layer 152 are silicon, silicon nitride, andsilicon oxide, for example. Suitable materials for the anchor layer 152can also be a material that is included in the piezoelectric layer 160,which in this case is aluminum nitride. Each PMUT (142, 144) includes afirst PMUT electrode (172, 174) positioned on a first side (bottomsurface) 164 of the piezoelectric layer 160 and a second PMUT electrode(182, 184) positioned on a second side (top surface) 166 opposite thefirst side. In each PMUT (142, 144), the first PMUT electrode (172,174), the second PMUT electrode (182, 184), and the piezoelectric layer160 between them constitute a piezoelectric capacitor. The first PMUTelectrodes (172, 174) and the second PMUT electrodes (182, 184) arecoupled to the signal processing circuitry 137. The cavities (172, 174)are positioned between the thin-film piezoelectric stack 162 and thesemiconductor substrate 150. In the example shown, the FMTSIC device 20is in the form of an encapsulated package 22. The cavities 192, 194 arepreferably under low pressure (pressure lower than atmospheric pressureor in vacuum) and remain so because of the package 22.

Each PMFE 146 includes a respective portion of the thin-filmpiezoelectric stack 162. Each PMFE 146 includes a first PMFE electrode176 positioned on a first side (bottom surface) 164 of the piezoelectriclayer 160 and a second PMFE electrode 186 positioned on a second side(top surface) 166 opposite the first side. In each PMFE 146, the firstPMFE electrode 176, the second PMFE electrode 186, and the piezoelectriclayer 160 between them constitute a piezoelectric capacitor. The PMFEsare coupled to the signal processing circuitry 137. In the exampleshown, the PMFE is not overlying any cavity.

The PMUT transmitter 142 is shown in cross section in FIGS. 5, 6, and 7.In the example shown, the thickness of the top mechanical layer 156 isgreater than the thickness of the bottom mechanical layer 154, and thetop mechanical layer 156 and the bottom mechanical layer 154 contain thesame material, aluminum nitride. In this case, the neutral axis 158 ispositioned within the top mechanical layer 156. The neutral axis is theaxis in the beam (in this case, the beam is the piezoelectric stack 162)along which there are no normal stresses or strains during bending. FIG.5 shows the PMUT transmitter in a quiescent state, in which there is novoltage applied between the first PMUT electrode 172 and the second PMUTelectrode 182. The piezoelectric layer 160 has a built-in polarization(piezoelectric polarization) that is approximately parallel to normaldirection 190. Normal direction 190 is normal to the piezoelectric layer160. Normal direction 190 is approximately normal to a plane of therespective piezoelectric capacitor. FIG. 6 shows the PMUT transmitter ina first transmitter state, in which there is a first transmitter voltageV_(Tx1) (corresponding to a certain polarity and magnitude) appliedbetween the electrodes (172, 182). As a result, the piezoelectric stack162 flexes upward (away from the cavity 192).

In FIG. 5, a portion 40 of the piezoelectric stack 162 overlying thecavity 192 is bendable whereas the other portions (66A, 66B) of thepiezoelectric stack 162 are anchored over the anchoring layer 152. FIG.4 is a schematic cross-sectional view of the bendable portion 40 of athin-film piezoelectric stack 162. For simplifying the discussion,individual electrodes and cover layers present in FIGS. 5 and 6 havebeen omitted. In the idealized case, the left edge (67A) and right edge(67B) of the illustrated portion 40 are anchored and cannot move. FIG. 4shows a first state, in which the piezoelectric stack 162 is flexedupward. A point of greatest deviation from the quiescent state islabeled 42 and corresponds approximately to a central point between theanchored edges (67A, 67B). At central point 42, there is the greatesttensile (positive) strain in a region 56 above the neutral axis 158 andthe greatest compressive (negative) strain in a region 58 below theneutral axis 158. Proceeding radially outward from the central point 42toward the anchored edges (67A or 67B), the tensile (positive) strain inthe region 56 above the neutral axis 158 decreases to 0 at theinflection point (44A or 44B). Proceeding radially outward from thecentral point 42 toward the anchored edges (67A or 67B), the compressive(negative) strain in the region 58 below the neutral axis 158 decreasesto 0 (becomes less negative and reaches 0) at the inflection point (44Aor 44B). Furthermore, in outer regions between the inflection point (44Aor 44B) and the anchored edges (67A or 67B), the polarities of thestrains are reversed. Specifically, in a region 62A, 62B above theneutral axis 158, the strain is compressive (negative), and in a region64A, 64B below the neutral axis 158, the strain is tensile (positive).The inflection point of a thin-film piezoelectric stack gives a lateralposition along the thin-film piezoelectric stack at which the stress is0. The stress changes sign (from negative to positive or positive tonegative) upon laterally traversing the inflection point. In a middleregion in between the inflection points of the piezoelectric stack,there is compressive (negative) strain in portions of the piezoelectricstack 162 below the neutral axis 158, including the piezoelectric layer160, and tensile (positive) strain in portions of the piezoelectricstack 162 above the neutral axis 158. In the first state, thepiezoelectric layer 160 is contracting or is in compression (negativestrain) in this middle region. In this middle region, the piezoelectriclayer is covered by the PMUT electrodes (172, 182).

FIG. 7 shows the PMUT transmitter in a second transmitter state, inwhich there is a second transmitter voltage V_(Tx2) (corresponding to acertain polarity and magnitude) applied between the PMUT electrodes(172, 182). In a middle region in between the inflection points of thepiezoelectric stack, there is tensile (positive) strain in portions ofthe piezoelectric stack 162 below the neutral axis 158, including thepiezoelectric layer 160, and compressive (negative) strain in portionsof the piezoelectric stack 162 above the neutral axis 158. As a result,the portion of the piezoelectric stack 162 overlying the cavity 192flexes downward (toward the cavity 192). The signal processing circuitry137 is operated to generate and apply a time-varying voltage signalV_(Tx)(t) between the PMUT electrodes (172, 182) of the PMUT transmitter142. If the time-varying voltage signal oscillates between the firsttransmitter voltage and the second transmitter voltage at a certainfrequency, the portion of the piezoelectric stack 162 oscillates betweenthe first transmitter state and the second transmitter state at thatfrequency. As a result, the PMUT transmitter generates (transmits), uponapplication of the time-varying voltage signal, ultrasound signalspropagating along the normal direction 190. Because of the presence ofthe cavity 192 at a low pressure, a relatively small fraction of thegenerated ultrasound energy is transmitted downward toward the cavity192, and a relatively large fraction of the generated ultrasound energyis transmitted upward away from the cavity 192. The PMUT transmittersare configured to transmit ultrasound signals of a frequency in a rangeof 0.1 MHz to 25 MHz.

The PMUT receiver 144 is shown in cross section in FIGS. 8, 9, and 10.FIG. 8 shows the PMUT receiver in a quiescent state, in which there isno flexing of the piezoelectric stack 162 away from or towards thecavity 194. In the quiescent state, there is no voltage generatedbetween the PMUT electrodes (174, 184). FIG. 9 shows the PMUT receiverin a first receiver state, in which a positive ultrasound pressure waveis incident on the PMUT receiver, along the normal direction 190, tocause the portion of the piezoelectric stack 162 overlying the cavity194 to flex downwards (towards the cavity 194). In a middle region inbetween the inflection points of the piezoelectric stack, there istensile (positive) strain in portions of the piezoelectric stack 162below the neutral axis 158, including the piezoelectric layer 160, andcompressive (negative) strain in portions of the piezoelectric stack 162above the neutral axis 158. As a result, a first receiver voltageV_(Rx1) (corresponding to a certain polarity and magnitude) is generatedbetween the PMUT electrodes (174, 184).

FIG. 10 shows the PMUT receiver in a second receiver state, in which anegative ultrasound pressure wave is incident on the PMUT receiver,along the normal direction 190, to cause the portion of thepiezoelectric stack 162 overlying the cavity 194 to flex upwards (awayfrom the cavity 194). In a middle region in between the inflectionpoints of the piezoelectric stack, there is compressive (negative)strain in portions of the piezoelectric stack 162 below the neutral axis158, including the piezoelectric layer 160, and tensile (positive)strain in portions of the piezoelectric stack 162 above the neutral axis158. As a result, a second receiver voltage V_(Rx2) (corresponding to acertain polarity and magnitude) is generated between the PMUT electrodes(174, 184). If ultrasound signals are incident on the PMUT receiver 144along the normal direction 190 causing the portion of the piezoelectricstack 162 to oscillate between the first receiver state and the secondreceiver state, a time-varying voltage signal V_(Rx)(t) oscillatingbetween the first receiver voltage and the second receiver voltage isgenerated between the PMUT electrodes (174, 184). The time-varyingvoltage signal is amplified and processed by the signal processingcircuitry 137.

In operation, the PMUT transmitter 142 is configured to transmit, uponapplication of voltage signals between the PMUT transmitter electrodes(172, 182), ultrasound signals of a first frequency F₁, in longitudinalmode(s) propagating along a normal direction 190 approximately normal tothe piezoelectric layer 160 away from the cavity 192 towards the senseregion 126. The ultrasound signals propagate towards the sense region126 of the cover layer 120 to which FMTSIC 20 is coupled. Uponapplication of the voltage signals, the respective portion of thepiezoelectric stack overlying the cavity 192 (of the PMUT transmitter142) oscillates with a first frequency F₁ between a first transmitterstate and a second transmitter state to generate ultrasound signals ofthe first frequency F₁. The PMUT receiver 144 is configured to output,in response to ultrasound signals of the first frequency F₁ arrivingalong the normal direction, voltage signals between the PMUT receiverelectrodes (174, 184). In response to ultrasound signals of the firstfrequency F₁ arriving along the normal direction, the portion of thethin-film piezoelectric stack 162 overlying the cavity oscillates at thefirst frequency F₁. Some fraction of the ultrasound signals transmittedby the PMUT transmitter 142 returns to the PMUT receiver 144 as an echoultrasound signal. In the use case illustrated in FIG. 1, the relativeamplitude or energy of the echo ultrasound signal depends upon thepresence of a digit (e.g., human finger) or other object (e.g., waterdrop) touching the sense region 126. If the sense region 126 is touchedby a digit or other object, there is greater attenuation of the echoultrasound signal than if there is no touching at the sense region 126.By amplifying and processing the time-varying voltage signal from thePMUT receiver at the signal processing circuitry, these touch events canbe detected.

A portion 130 of the FMTSIC 20 containing a PMFE 146 is shown in crosssection in FIG. 11. Also shown is the ASIC portion 136 that is under thePMFE 146 and the encapsulating adhesive 32 that is above the PMFE 146.FIG. 11 shows the PMFE in a quiescent state, in which there is noflexing of the piezoelectric stack 162. In the quiescent state, there isno voltage generated between the PMFE electrodes (176, 186).

FIGS. 12, 13, and 14 are schematic side views of an FMTSIC 20 and acover layer 120 attached to or adhered to (coupled to) each other. A topsurface (ultrasound transmission surface) 26 of FMTSIC 20 is coupled toinner surface 122 of the cover layer 120. FMTSIC 20 and cover layer 120overlie a rigid substrate 135. For ease of viewing, other components ofapparatus 100 (e.g., flexible circuit substrate 108, ICs 114) have beenomitted. FMTSIC 20 includes PMFEs 146. In the examples shown, two anchorposts 131, 133 fix the two ends of the cover layer 120 to the substrate135.

In the example of FIG. 12, FMTSIC 20 is not anchored to the rigidsubstrate 135 and can move with the cover layer 120 when the cover layer120 is deflected upwards or downwards. A downward force 117, shown as adownward arrow, is applied by a digit (or another object) pressingagainst the outer surface 124 of the cover layer 120 at the sense region126 for example. A digit pressing against or tapping the outer surface124 are examples of touch excitation, or more generally, excitation. Inthe example shown in FIG. 12, the cover layer 120 is deflected in afirst direction (e.g., downwards) in response to a touch excitation atthe sense region 126. FMTSIC 20 is located approximately half-waybetween the anchor posts 131, 133 and sense region 126 overlaps FMTSIC20. A neutral axis 125 is located within the cover layer 120. A lowerportion 127 of the cover layer 120, below the neutral axis 125, is undertensile (positive) strain at the sense region 126, represented byoutward pointing arrows, primarily along lateral direction 191,perpendicular to the normal direction 190. The lateral direction 191 isapproximately parallel to the piezoelectric layer 160 at the respectivelocation of the piezoelectric layer 160 (at region 126). An upperportion 129 of the cover layer 120, above the neutral axis 125, is undercompressive (negative) strain at the sense region 126, represented byinward pointing arrows, primarily along lateral direction 191. SinceFMTSIC 20 is coupled to the inner surface 122, adjacent to the lowerportion 127, the PMFEs 146 are also under tensile (positive) strain.Typically, the entire FMTSIC 20 may be deflected under the applieddownward force 117. In the example shown in FIG. 12, the PMFEs 146 areunder a positive strain, and the respective portions of thepiezoelectric layer 160 at the PMFEs 146 undergo expansion along alateral direction 191. As a result, an electrical charge is generated ateach PMFE (146) between the respective PMFE electrodes (176, 186). Thiselectrical charge is detectable as a first deflection voltage V_(d1)(corresponding to strain of a certain polarity and magnitude). Thepolarity of the first deflection voltage V_(d1) at a PMFE depends uponthe polarity of the strain (positive strain (tensile) or negative strain(compressive)) at the respective portion of the piezoelectric layerbetween the respective PMFE electrodes of the PMFE. The magnitude of thefirst deflection voltage V_(d1) at a PMFE depends upon the magnitude ofthe strain at the respective portion of the piezoelectric layer betweenthe respective PMFE electrodes of the PMFE. Subsequently, when thedownward force 117 is no longer applied to the sense region 126, thecover layer 120 deflects in a second direction opposite the firstdirection (e.g., upwards). This is detectable as a second deflectionvoltage V_(d2) (corresponding to strain of a certain polarity andmagnitude). The polarity of the second deflection voltage V_(d2) at aPMFE depends upon the polarity of the strain at the respective portionof the piezoelectric layer between the respective PMFE electrodes of thePMFE. The magnitude of the second deflection voltage V_(d2) at a PMFEdepends upon the magnitude of the strain at the respective portion ofthe piezoelectric layer between the respective PMFE electrodes of thePMFE.

FIG. 12 shows a second FMTSIC 20A, including PMFEs 146A. A top surface(ultrasound transmission surface) 26A of FMTSIC 20A is coupled to innersurface 122 of the cover layer 120. FMTSIC 20A overlies the rigidsubstrate 135 and is located at a second region 126A, between anchorpost 131 and first FMTSIC 20. Note that FMTSIC 20A is laterallydisplaced from the location where the downward force 117 is applied tothe outer surface 124 (at sense region 126). The lower portion 127 ofthe cover layer 120 is under compressive (negative) strain at the secondregion 126A, represented by inward pointing arrows, primarily along thelateral direction 191A, perpendicular to the normal direction 190A. Thelateral direction 191A is approximately parallel to the piezoelectriclayer 160 at the respective location of the piezoelectric layer 160 (atsecond region 126A). The upper portion 129 of the cover layer 120 isunder tensile (positive) strain at the second region 126A, representedby outward pointing arrows, primarily along the lateral direction 191A.Since FMTSIC 20A is coupled to the inner surface 122, adjacent to thelower portion 127, the PMFEs 146A are also under compressive (negative)strain. These examples illustrate that when the cover layer and theFMTSICs undergo deflection in response to a touch excitation at theouter surface, expansion and/or compression of the piezoelectric layeralong the lateral direction may be induced by the deflection of thecover layer.

In the example shown in FIG. 13, the bottom surface 24 of FMTSIC 20 isanchored to the rigid substrate 135. When downward force 117 is appliedto the outer surface 124 of the cover layer 120 at sense region 126, theportion of the cover layer 120 at the sense region 126 transmits thedownward force along normal direction 190. The portion of the coverlayer 120 at the sense region 126 and the FMTSIC 20 undergo compressionalong normal direction 190. Consequently, the PMFEs 146 includingpiezoelectric layer 160 are compressed along the normal direction 190,approximately normal to the piezoelectric layer 160. As a result, anelectrical charge is generated between the PMFE electrodes (176, 186).This electrical charge is detectable as a voltage V_(c) (correspondingto a strain of a certain polarity and magnitude) between the PMFEelectrodes. The downward force 117 that causes this compression isapplied during a touch excitation, such as tapping at or pressingagainst the outer surface 124. The pressing or the tapping can berepetitive. Typically, the entire FMTSIC 20 may undergo compression.Subsequently, the piezoelectric layer 160 relaxes from the compressedstate. In other cases, there may also be compression along a lateraldirection 191, or along other directions.

In the example shown in FIG. 14, FMTSIC 20 is not anchored to the rigidsubstrate 135. A downward force 139, shown as a downward arrow, isapplied to the outer surface 124 of the cover layer 120 at the senseregion 126. The downward force 139 is generated as a result of an impactof touch excitation at the sense region 126. For example, the downwardforce 139 is generated as a result of the impact of a digit (or anotherobject) tapping the outer surface at the sense region 126. The touchexcitation (e.g., tapping) can be repetitive. The impact of the touchexcitation (e.g., tapping) generates elastic waves that travel outwardfrom the location of the impact (on the outer surface 124 at senseregion 126) and at least some of the elastic waves travel toward theinner surface 122. Accordingly, at least some portion 149 of the elasticwaves are incident on the FMTSIC 20.

In general, an impact of a touch excitation (e.g., tapping) on a surfaceof a stack (e.g., cover layer) can generate different types of wavesincluding pressure waves, shear waves, surface waves and Lamb waves.Pressure waves, shear waves, and surface waves are in a class of wavescalled elastic waves. Pressure waves (also called primary waves orP-waves) are waves in which the molecular oscillations (particleoscillations) are parallel to the direction of propagation of the waves.Shear waves (also called secondary waves or S-waves) are waves in whichthe molecular oscillations (particle oscillations) are perpendicular tothe direction of propagation of the waves. Pressure waves and shearwaves travel radially outwards from the location of impact. Surfacewaves are waves in which the energy of the waves are trapped within ashort depth from the surface and the waves propagate along the surfaceof the stack. Lamb waves are elastic waves that can propagate in plates.When an object (e.g., a finger) impacts a surface of a stack, differenttypes of elastic waves can be generated depending upon the specifics ofthe impact (e.g., speed, angle, duration of contact, details of thecontact surface), the relevant material properties (e.g., materialproperties of the object and the stack), and boundary conditions. Forexample, pressure waves can be generated when an impact of a touchexcitation at the outer surface is approximately normal to the outersurface. For example, shear waves can be generated when an impact of atouch excitation at the outer surface has a component parallel to theouter surface, such as a finger hitting the outer surface at an obliqueangle or a finger rubbing against the outer surface. Some of theseelastic waves can propagate towards the FMTSIC 20 and PMFEs 146. If thestack is sufficiently thin, then some portion of surface waves canpropagate towards the FMTSIC 20 and PMFEs 146 and be detected by thePMFEs 146.

Accordingly, when elastic waves 149 are incident on the FMTSIC 20 andPMFEs 146, the elastic waves induce time-dependent oscillatorydeformation to the piezoelectric layer 160 at the PMFE 146. Thisoscillatory deformation can include: lateral deformation (compressionand expansion along the lateral direction 191 approximately parallel topiezoelectric layer 160), normal deformation (compression and expansionalong the normal direction 190 approximately normal to the piezoelectriclayer 160), and shear deformation. As a result, time-varying electricalcharges are generated at each PMFE (146) between the respective PMFEelectrodes (176, 186). These time-varying electrical charges aredetectable as time-varying voltage signals. The signal processingcircuitry amplifies and processes these time-varying voltage signals.Typically, the time-dependent oscillatory deformations induced by animpact of a touch excitation are in a frequency range of 10 Hz to 1 MHz.For example, suppose that elastic waves 149 include pressure wavesincident on the PMFEs 146 along the normal direction 190; these pressurewaves may induce compression (under a positive pressure wave) andexpansion (under a negative pressure wave) of the piezoelectric layer160 along the normal direction 190. As another example, suppose thatelastic waves 149 include shear waves incident on the PMFEs 146 alongthe normal direction 190; these shear waves may induce compression andexpansion of the piezoelectric layer 160 along the lateral direction191.

Consider another case in which a downward force 139A, shown as adownward arrow, is applied to the outer surface 124 at a second region126A, between anchor post 131 and FMTSIC 20. The downward force 139A isgenerated as a result of an impact of touch excitation at the secondregion 126A. The impact of the touch excitation generates elastic wavesthat travel outward from the location of the impact (region 126A) and atleast some of the elastic waves travel towards the inner surface 122.Accordingly, at least some portion 149A of the elastic waves areincident on the FMTSIC 20, causing the piezoelectric layer 160 toundergo time-dependent oscillatory deformation. As a result,time-varying electrical charges are generated at each PMFE (146) betweenthe respective PMFE electrodes (176, 186). These time-varying electricalcharges are detectable as time-varying voltage signals, although theimpact of the touch excitation occurred at a second region 126A that islaterally displaced from the sense region 126.

Elastic waves 149A that reach FMTSIC 20 from region 126A may be weaker(for example, smaller in amplitude) than elastic waves 149 that reachFMTSIC 20 from sense region 126, because of a greater distance betweenthe location of impact and the FMTSIC. An array of PMFEs can beconfigured to be a position-sensitive input device, sensitive to alocation of the impact (e.g., tapping) of a touch excitation. An arrayof PMFEs can be an array of PMFEs in a single FMTSIC or arrays of PMFEsin multiple FMTSICs. For example, a table input apparatus could have anarray of FMTSICs located at respective lateral positions underneath thetable's top surface, in which each FMTSIC would contain at least onePMFE and preferably multiple PMFEs. The signal processing circuitry canbe configured to amplify and process the time-varying voltage signalsfrom the PMFEs and analyze some features of those time-varying voltagesignals. Examples of features of time-varying voltage signals are: (1)amplitudes of the time-varying voltage signals, and (2) the relativetiming of time-varying voltage signals (the “time-of-flight”). Forexample, a PMFE exhibiting a shorter time-of-flight is closer to thelocation of impact than another PMFE exhibiting a longer time-of-flight.The signal processing circuitry can analyze features of time-varyingsignals (e.g., amplitude and/or time-of-flight) from the PMFEs in anarray of PMFEs to estimate a location of impact of a touch excitation.

In operation, PMFE 146 is configured to output voltage signals betweenthe PMFE electrodes (176, 186) in accordance with a time-varying strainat the respective portion of the piezoelectric layer between the PMFEelectrodes (176, 186) resulting from a low-frequency mechanicaldeformation. A touch excitation at the cover layer or at anothercomponent mechanically coupled to the cover layer causes a low-frequencymechanical deformation (of the cover layer or other component at thepoint of excitation). The touch excitation induces effects includingdeflection (as illustrated in FIG. 12), compression (as illustrated inFIG. 13), and/or elastic-wave oscillations (as illustrated in FIG. 14).In an actual touch event, more than one of these effects may beobservable. Consider tapping by a finger as an example of a touchexcitation. As the finger impacts the outer surface 124, elastic wavesare generated which are detectable as time-varying voltage signals atthe PMFEs (FIG. 14). Elastic waves are generated by the impact of thetouch excitation. Subsequently, as the finger presses against the coverlayer, the FMTSIC undergoes deflection (FIG. 12). There is expansion orcompression of the piezoelectric layer along a lateral direction. Thelow-frequency mechanical deformation can be caused by a digit pressingagainst or tapping at outer surface of the cover layer 120, to which theFMTSIC 20 is attached (coupled). The PMFE 146 is coupled to the signalprocessing circuitry 137. By amplifying and processing the voltagesignals from the PMFE at the signal processing circuitry, the strainthat results from the mechanical deformation of the piezoelectric layercan be measured.

It is possible to adjust the relative amplitudes of the PMFE voltagesignals attributable to the elastic-wave oscillations (FIG. 14) andlateral expansion and compression due to deflection (FIG. 12). Forexample, one can choose the cover layer to be more or less deformable.For example, the cover layer 120 of FIG. 14 may be thicker and/or madeof more rigid material than the cover layer 120 of FIG. 12.

PMFE 146 is configured to output voltage signals between the PMFEelectrodes (176, 186) in accordance with a time-varying strain at therespective portion of the piezoelectric layer between the PMFEelectrodes (176, 186) resulting from a low-frequency mechanicaldeformation. Typically, the low-frequency deformation is induced bytouch excitation which is not repetitive (repetition rate is effectively0 Hz) or is repetitive having a repetition rate of 100 Hz or less, or 10Hz or less. These repetition rates correspond to the repetition rates ofa repetitive touch excitation, e.g., a digit repeatedly pressing againstor tapping the sense region. An example of a repetition rate calculationis explained with reference to FIG. 37 and FIG. 38.

A touch excitation, or more generally, excitation can occur somewhereother than at the sense region. Consider an implementation of FMTSICs ina portable apparatus, such as a smartphone. In some cases, the coverlayer, to which the FMTSIC is coupled, can be a portion of thesmartphone housing, and in other cases, the housing and the cover layercan be attached to each other, such that forces applied to the housingcan be transmitted to the cover layer. We can refer to both cases as acomponent (e.g., housing) being mechanically coupled to the cover layer.Excitation such as bending of, twisting of, pinching of, typing at, andtapping at the housing can also cause low-frequency mechanicaldeformation. For example, typing at the housing can include typing at atouch panel of the smartphone. There can be a time-varying strain(force) at a respective portion of the piezoelectric layer at a PMFEresulting from this low-frequency deformation.

An FMTSIC can contain multiple PMUT transmitters, PMUT receivers, andPMFEs. FIG. 15 is a top view of a MEMS portion 200 of an FMTSIC device.The PMUTs (PMUT transmitters 204 shown as white circles and PMUTreceivers 206 shown as grey circles) are arranged in a two-dimensionalarray, extending along the X-axis (220) and Y-axis (222). The PMUTs arearranged in columns (A, B, C, and D) and rows (1, 2, 3, and 4). In theexample shown, the two-dimensional PMUT array 202 has a square outerperimeter, but in other examples the outer perimeter can have othershapes such as a rectangle. In the example shown, the total number ofPMUTs is 16, of which 12 are PMUT transmitters 204 and 4 are PMUTreceivers 206. In this example, the PMUT receivers number less than thePMUT transmitters. The PMUTs are shown as circles because the overlaparea of the first (bottom) electrode 172 and the second (top) electrode174 is approximately circular. In other examples, the overlap area canhave other shapes, such as a square. In the example shown, the PMUTs areof the same lateral size (area), but in other examples PMUTs ofdifferent sizes are also possible.

The PMUT transmitters 204 are configured to transmit, upon applicationof voltage signals between the respective first PMUT electrode and therespective second PMUT electrode, ultrasound signals of a firstfrequency F₁, in longitudinal mode(s) propagating along a normaldirection approximately normal to the piezoelectric stack away from thecavities and towards the sense region. A benefit to a two-dimensionalarray of PMUT transmitters is that by optimization of the voltagesignals to each of the PMUT transmitters, the transmitted ultrasoundsignals can be made to interfere constructively to achieve abeam-forming effect if desired. The PMUT receivers 206 are configured tooutput, in response to ultrasound signals of the first frequency F₁arriving along the normal direction, voltage signals between therespective first PMUT electrode and the respective second PMUTelectrode. A benefit to a two-dimensional array of PMUT receivers isthat the array could achieve two-dimensional positional resolution of atouch event. For example, in the use case shown in FIG. 1, a finger 118is touching the cover layer 120 at a sense region 126. In particular,the finger has ridges 119 and corresponding valleys in between theridges. Therefore, some of the PMUT receivers might receive echoultrasound signals that have undergone greater attenuation at the ridges119, and some others of the PMUT receivers might receive echo ultrasoundsignals that have undergone lesser attenuation at the valleys in betweenthe ridges 119.

The MEMS portion includes four PMFEs (214, locations identified as p, q,r, and s) arranged in a two-dimensional array 212. The PMFE array 212has an opening, which is devoid of PMFEs, in which the PMUT array 202 isdisposed. In the example shown, there are PMFEs to the left of (p and q)and to the right of (r and s) of the PMUT array 202. Each PMFE measuresan applied force at a different X and Y location. Therefore, the PMFEarray 212 achieves a two-dimensional positional resolution of appliedforces measurement. An advantage to combining the touch-sensing (PMUTs)and force-measuring (PMFEs) functions into one integrated circuit deviceis that it becomes possible to distinguish between stationary objectsthat touch but do not apply significant force (e.g., water droplet onsense region 126) and moving objects that touch and apply significantforce (e.g., finger).

FIG. 16 is a top view of a MEMS portion 230 of an FMTSIC device. ThePMUT array 202 is identical to that illustrated in FIG. 15. The MEMSportion includes a PMFE array 232 containing eight PMFEs (234). ThePMFEs are arranged into four sets (240, 242, 244, and 246), where eachset is associated with a different X and Y location. Therefore, the PMFEarray 232 achieves a two-dimensional positional resolution of appliedforces measurement. Each PMFE set contains two PMFEs. In the exampleshown, set 240 contains p1 and p2, set 242 contains q1 and q2, set 244contains r1 and r2, and set 246 contains s1 and s2. Note that in eachset, the two PMFEs are laid side-by-side in the X-direction. The PMFEsin a set are electrically connected to each other. The electricalconnections among the PMFEs in a set are described in detailhereinbelow, with reference to FIGS. 23, 24, and 25.

FIG. 17 is a top view of a MEMS portion 250 of an FMTSIC device. ThePMUT array 202 is identical to that illustrated in FIGS. 15 and 16. TheMEMS portion includes a PMFE array 252 containing eight PMFEs (254). ThePMFEs are arranged into four sets (260, 262, 264, and 266), where eachset is associated with a different X and Y location. Therefore, the PMFEarray 252 achieves a two-dimensional positional resolution of appliedforces measurement. This capability is similar to that of PMFE array232. Each PMFE set contains two PMFEs. In the example shown, set 260contains t1 and t2, set 262 contains u1 and u2, set 264 contains v1 andv2, and set 246 contains w1 and w2. PMFE array 252 is similar to PMFEarray 232 in the total number of PMFEs, the number of PMFE sets, and thenumber of PMFEs in each set. Note that the size of each PMFE is smallerthan in FIG. 16, making it possible to arrange two PMFEs in each setside-by-side in the Y-direction. As a result, the overall footprint ofMEMS portion 250 is smaller than that of MEMS portion 230. It ispreferable that each PMFE has lateral dimensions no greater than 2.5 mmby 2.5 mm.

FIG. 18 is a schematic top view of a PMUT array 270. The PMUTs (PMUTtransmitters 274 shown as white circles and PMUT receivers 276 shown asgrey circles) are arranged in a two-dimensional array, extending alongthe X-axis (220) and Y-axis (222). The PMUTs are arranged in twelvecolumns (A through L) and twelve rows (1 through 12). The PMUT array 270has a square outer perimeter. The total number of PMUTs is 144, of which128 are PMUT transmitters 274 and 16 are PMUT receivers 276. The PMUTreceivers number less than the PMUT transmitters. A circle 272 is drawnaround a central point 278 of the PMUT array 270, to help identifypoints that are approximately equidistant from the central point 278.The circle 272 intersects all of the PMUT receivers 276. Accordingly,all of the receivers 276 are approximately equidistant from the centralpoint 278.

FIG. 19 is a schematic top view of a PMUT array 280. Array 280 isidentical to array 270 except that sixteen PMUT transmitters near thecentral point 278 have been removed. The PMUT transmitters are missingfrom central area 282 corresponding to columns E, F, G, and H, and rows5, 6, 7, and 8. Accordingly, the total number of PMUTs is 128, of which112 are PMUT transmitters 274 and 16 are PMUT receivers 276. The PMUTreceivers number less than the PMUT transmitters. Note that the array280 has a square outer perimeter. Central area 282 which is devoid ofPMUTs can be used as space for interconnect vias in the MEMS portion 134(FIG. 3).

The PMUT arrays shown in FIGS. 15, 16, 17, 18, and 19 illustrateexamples of PMUT arrays configured to operate at a single frequency F₁,in which the PMUT transmitters transmit ultrasound signals at F₁ and thePMUT receivers are configured to receive ultrasound signals at frequencyF₁. FIGS. 20, 21, and 22 are schematic top views of PMUT arrays that areconfigured to operate at frequencies F₁ and F₂. In each of FIGS. 20, 21,and 22, a PMUT array (290, 310, 330) contains first PMUT transmitters(294, 314, 334, shown as grey circles) configured to transmit ultrasoundsignals at a first frequency F₁, first PMUT receivers (296, 316, 336,shown as diagonal hatch-patterned circles) configured to receiveultrasound signals at a first frequency F₁, second PMUT transmitters(304, 324, 344, shown as horizontal hatch-patterned circles) configuredto transmit ultrasound signals at a second frequency F₂, and second PMUTreceivers (306, 326, 346, shown as white circles) configured to receiveultrasound signals at a second frequency F₂. In each of FIGS. 20, 21,and 22, PMUTs are missing from a central area corresponding to columns Fand G and rows 6 and 7. The counts of the first PMUT transmitters, firstPMUT receivers, second PMUT transmitters, and the second PMUT receiversare tabulated in Table 1. In each case, the first receivers number lessthan the first transmitters and the second receivers number less thanthe second transmitters.

TABLE 1 FIG. 1st 1st 2nd 2nd No. Transmitter Receiver TransmitterReceiver Total 20 56 8 56 20 140 21 48 16 56 20 140 22 48 16 60 16 140

In each of FIGS. 20, 21, and 22, a larger circle (292, 312, 332) and asmaller circle (302, 322, 342) are drawn around a central point (298,318, 338) of the PMUT array (290, 310, 330) to help identify points thatare approximately equidistant from the central point (298, 318, 338).The first transmitters and receivers are contained in the four cornerquadrants (4 columns by 4 rows each) remote from the central point,corresponding to columns A, B, C, D, I, J, K, and L and rows 1, 2, 3, 4,9, 10, 11, 12. The second transmitters and receivers are contained inthe remaining space. In the case of FIGS. 20 and 21, all of the firstreceivers (296, 316) intersect the larger circle (292, 312).Accordingly, the first receivers (296, 316) are approximatelyequidistant from the central point (298, 318). In the case of FIG. 22,half of the first receivers 336 intersect the larger circle 332, andanother half of the first receivers 336 are adjacent to other firstreceivers 336 that intersect the larger circle 332. Accordingly, thefirst receivers 336 are approximately equidistant from the central point338. In each of FIGS. 20, 21, and 22, the second receivers (306, 326,346) intersect the smaller circle (302, 322, 342) or are adjacent toother second receivers (306, 326, 346) that intersect the smaller circle(302, 322, 342). Accordingly, the second receivers (306, 326, 346) areapproximately equidistant from the central point (298, 318, 338). Onaverage, the second receivers (306, 326, 346) are closer than the firstreceivers (296, 316, 336) to the central point (298, 318, 338) of thePMUT array (290, 310, 330).

If the cover layer 120 is at room temperature (approximately 25° C.) anda human finger (approximately 37° C.) touches it at the sense region126, temperatures in the sense region 126 and surrounding areas,including the FMTSICs (102, 106), might increase. There is likely to betemperature-induced drift in the ultrasound signal measured at the PMUTreceivers. In order to reduce the effect of this temperature-induceddrift, it is preferable to operate the PMUT transmitters and PMUTreceivers at two different frequencies F₁ and F₂, because thetemperature-dependent drift characteristics will be different atdifferent frequencies F₁ and F₂. Both frequencies F₁ and F₂ arepreferably in a range of 0.1 MHz to 25 MHz. In order to minimizetemperature-induced drift, the frequencies F₁ and F₂ are preferablysufficiently different from each other such that thetemperature-dependent drift characteristics will be sufficientlydifferent from each other. On the other hand, suppose that the firsttransmitters operate at a first central frequency F₁ with a bandwidthΔF₁, and the second transmitters operate at a second central frequencyF₂ with a bandwidth ΔF₂, with F₁<F₂. If the frequencies and bandwidthsare selected such that F₁+ΔF₁/2 is greater than F₂−ΔF₂/2 (the first andsecond bands overlap), then the power transmitted by the first andsecond transmitters will be additive. Accordingly, there are operationaladvantages to selecting the frequencies F₁ and F₂ to be sufficientlyclose to each other.

FIG. 23 shows a flow diagram 350 for the process of making an FMTSICdevice 20 and an apparatus 100. The method includes steps 352, 354, 356,and 358. At step 352, the ASIC portion 136 including signal processingcircuitry 137 is fabricated on a semiconductor substrate (wafer) 150using a CMOS fabrication process. At step 354, the MEMS portion 134 isfabricated on top of the ASIC portion 136. At step 356, the integratedcircuit device, FMTSIC 20, is made. This step 356 includes, for example,the singulation of the wafer into dies, the mounting of dies onto apackage substrate, and the packaging of the die including application ofan epoxy adhesive. The making of FMTSICs is complete at the end of step356. Subsequently, an apparatus is made at step 358.

For example, the apparatus can be a mobile appliance (e.g., Smartphone,tablet computer, laptop computer), a household appliance (e.g., washingmachine, drier, light switches, air conditioner, refrigerator, oven,remote controller devices), a medical appliance, an industrialappliance, an office appliance, an automobile, or an airplane, or acomponent of any of the above. This step 358 includes, for example, themounting of one or more FMTSIC devices and other ICs to a flexiblecircuit substrate and/or printed circuit board (PCB) and adhering theFMTSIC devices to an interior surface of a cover layer of the apparatus.

Step 358 may include a testing procedure carried out on PMFE(s) afteradhering the FMTSIC device(s) to the interior surface of the coverlayer. This testing procedure preferably includes the application of atesting force, in a range of 0.5 N to 10 N at the sense region. Forexample, suppose that upon application of a testing force of 7.5 N, amagnitude of the PMFE digital data (difference between maximum PMFEdigital data (e.g., 1042 in FIG. 37) and minimum PMFE digital data(e.g., 1044 in FIG. 38)) is 1280 LSB. It is possible to calculate one orboth of the following: (1) a ratio A of a magnitude of the PMFE digitaldata to a physical force value; and/or (2) a ratio B of a physical forcevalue to a magnitude of the PMFE digital data. In this example, theratio A=1280 LSB/7.5 N and the ratio B=7.5 N/1280 LSB. These ratios Aand B permit a conversion between PMFE digital data (expressed in LSB)and a physical force value (expressed in Newtons). These ratios A and/orB can be stored in a memory store (non-volatile memory) of therespective FMTSIC device.

Step 358 may include a testing procedure carried out on PMUT(s) afteradhering the FMTSIC device(s) to the interior surface of the coverlayer. This testing procedure preferably includes contacting an objectto the sense region (touch event) in which a force, in a range of 0.5 Nto 10 N, is applied at the sense region. For example, suppose that uponcontacting an object in which a testing force of 7.5 N is applied, thePMUT digital data decrease by 230 LSB (e.g., from the baseline 926 to aminimum signal 930 in FIG. 36). Accordingly, the dynamic range(difference between baseline and minimum signal) is 230 LSB underapplication of a testing force of 7.5 N. These dynamic range and testingforce data can be stored in a memory store (non-volatile memory) of therespective FMTSIC device.

FIG. 24 is an electronics block diagram of the FMTSIC device 20,including a MEMS portion 134 and signal processing circuitry 137. TheMEMS portion includes PMUT transmitters 142, PMUT receivers 144, andPMFEs 146. Signal processing circuitry 137 includes a high-voltagedomain 380 and a low-voltage domain 390. The high-voltage domain iscapable of operating at higher voltages required for driving the PMUTtransmitters. The high-voltage domain includes high-voltage transceivercircuitry 382, including high-voltage drivers. The high-voltagetransceiver circuitry 382 is connected to the first PMUT electrodes andthe second PMUT electrodes of the PMUT transmitters, via electricalinterconnections (wiring) 384. The high-voltage transceiver isconfigured to output voltage pulses of 5 V or greater, depending on therequirements of the PMUT transmitters. The processing circuit blocks 408are electrically connected to the high-voltage transceiver circuitry 382and the ADCs (396, 406). The processing circuit blocks 408 generatetime-varying signals that are transmitted to the high-voltagetransceiver circuitry 382. The high-voltage transceiver circuitry 382transmits high-voltage signals to the PMUT transmitters 142 inaccordance with the time-varying signals from the processing circuitblocks 408.

The low-voltage domain 390 includes amplifiers (392, 402) andanalog-to-digital converters (ADCs) (396, 406). The processing circuitblocks 408 are also contained in the low-voltage domain 390. Voltagesignals output by the PMUT receivers 144 (represented by gray circles)reach amplifiers 402 via electrical interconnections (wiring) 404 andget amplified by the amplifiers 402. The amplified voltage signals aresent to ADC 406 to be converted to digital signals which can beprocessed or stored by processing circuit blocks 408. Similarly, voltagesignals output by PMFEs 146 reach amplifiers 392 via electricalinterconnections (wiring) 394 and get amplified by the amplifiers 392.These amplified voltage signals are sent to ADC 396 to be converted todigital signals which can be processed or stored by processing circuitblocks 408. The processing circuit blocks 408 could be microcontrollers(MCUs), memories, and digital signal processors (DSPs), for example. Thewiring (384, 394, 404) traverses the semiconductor substrate, whichcontains the signal processing circuitry 137, and the MEMS portion 134,which contains the PMFEs 146, the PMUT transmitters 142, and the PMUTreceivers 144.

In the example shown (FIG. 24), the piezoelectric capacitorsconstituting the PMUT receivers 144 are connected to each other inparallel. Since the capacitances of these PMUT receivers are addedtogether, this arrangement of PMUT receivers is less sensitive to theeffects of parasitic capacitance. Accordingly, there is a unifiedvoltage signal transmitted from the PMUT receivers 144 to the amplifiers402. The piezoelectric capacitors constituting the PMUT transmitters 142are connected in parallel. Accordingly, there is a time-varying signaltransmitted from the high-voltage transceiver circuitry 382 to the PMUTtransmitters 142. The PMFEs 146 are grouped into two sets (p and q onthe left side, r and s on the right side), and the PMFEs in each set areconnected to each other in series. Accordingly, there are two sets ofPMFE signals transmitted from the PMFEs 146 to the amplifiers 392.

FIG. 25 is a schematic cross-sectional view of a set 500 of PMFEs 510and 520. Also shown is the ASIC portion 136 that is under the PMFEs 510,520 and the encapsulating adhesive 32 that is above the PMFEs 510 and520. FIG. 25 shows the PMFE in a quiescent state analogous to thequiescent state described with reference to FIG. 11. A PMFE wasdescribed with reference to FIG. 11. In the example shown, thepiezoelectric stack includes a piezoelectric layer 160, a top mechanicallayer 156, and a bottom mechanical layer 154. In a deformed state (shownin FIGS. 12, 13, and 14, for example), an electrical charge is generatedbetween the PMFE electrodes 512 and 514 of first PMFE 510 and betweenthe PMFE electrodes 522 and 524 of the second PMFE 520.

For each PMFE (510, 520), the first PMFE electrode (512, 522), thesecond PMFE electrode (514, 524), and the piezoelectric layer 160between them constitute a piezoelectric capacitor. FIG. 26 is a blockdiagram illustrating the electrical connections of the PMFE set (pair)to certain portions of the signal processing circuitry 137. In FIG. 26,we illustrate each PMFE (510, 520) as a piezoelectric capacitor. PMFEs510 and 520 are connected in series via a wire 516 that includes a viathat penetrates the piezoelectric layer 160 (FIG. 25). Wire 516 connectssecond electrode (top electrode) 514 of first PMFE 510 to the firstelectrode (bottom electrode) 522 of the second PMFE 512. The outermostelectrodes of the PMFE electrodes in the series 502 are first electrode512 of the first PMFE 510 and the second electrode 524 of the secondPMFE 520. These outermost electrodes of the first PMFE electrodes andthe second PMFE electrodes of the PMFEs in the series 502 are connectedas differential inputs 551, 552 to the amplifier circuitry 392 of thesignal processing circuitry 137. The voltage signals at inputs 551, 552are amplified by the amplifier circuitry 392. Amplified voltage signals420 are output from the amplifier circuitry 392 to the analog-to-digitalconverter (ADC) 396. Digital signals 430 are output from the ADC 396.

As shown in the example of FIG. 26, wire 516 is tied to a common node518. In this case, we can refer to the node between the two adjacentPMFEs 510, 520 connected in series as a common node. If the voltage ofthe common node is held at 0 V, the voltage signal input to input 551can be expressed as −ΔV₁, and the voltage signal input to input 552 canbe expressed as ΔV₂, where the subscripts refer to the first PMFE (510)or second PMFE (520). An advantage of a node between adjacent PMFEsconnected in series being a common node is that voltage offsets from thecommon node voltage are reduced, simplifying subsequent amplification oflow-voltage signals.

FIG. 27 is a block diagram illustrating the electrical connections of aPMFE set (600) to certain portions of the signal processing circuitry137. FIG. 27 is similar to FIG. 26 except that there are four PMFEs inthe set and these four PMFEs are connected in series. The secondelectrode 614 of the first PMFE 610 is connected to the first electrode622 of the second PMFE 620, the second electrode 624 of the second PMFE620 is connected to the first electrode 632 of the third PMFE 630, andthe second electrode 634 of the third PMFE 630 is connected to the firstelectrode 642 of the fourth PMFE 640. The outermost electrodes of thePMFE electrodes in the series 602 are first electrode 612 of the firstPMFE 610 and the second electrode 644 of the fourth PMFE 640. Theseoutermost electrodes of the PMFE electrodes in the series 602 areconnected as differential inputs 651, 652 to the amplifier circuitry 392of the signal processing circuitry 137. The voltage signals at inputs651, 652 are amplified by the amplifier circuitry 392. Amplified voltagesignals 420 are output from the amplifier circuitry 392 to theanalog-to-digital converter (ADC) 396. Digital signals 430 are outputfrom the ADC 396.

Wire 616 connects the second electrode 624 of the second PMFE 620 to thefirst electrode 632 of the third PMFE 630. Wire 616 is tied to a commonnode 618. If the voltage of the common node is held at 0 V, the voltagesignal input to input 651 can be expressed as −ΔV₁−ΔV₂, and the voltagesignal input to input 652 can be expressed as ΔV₃+ΔV₄, where thesubscripts refer to the first PMFE (610), second PMFE (620), third PMFE(630), and fourth PMFE (640).

FIG. 28 is a schematic top view of a PMUT 700, including a second PMUTelectrode (top PMUT electrode) 714, shown as a dark grey circular regioncentered around a central point 42. An inflection line 44 of thethin-film piezoelectric stack is shown is shown as a circle centeredaround the central point 42, located outside of the top PMUT electrode714. Inflection line 44 is analogous to the inflection point 44A, 44Bdiscussed in the context of the cross-sectional view of thepiezoelectric stack (FIG. 4). Since the strain changes sign (positive tonegative or negative to positive) upon laterally traversing theinflection line 44, it is preferable that the first PMUT electrode andthe second PMUT electrode be located inside the inflection line. In theexample shown, the top PMUT electrode (second PMUT electrode) is locatedwithin the inflection line (circle) 44. The bottom PMUT electrode (firstPMUT electrode), which is hidden behind the top PMUT electrode, is alsolocated within the inflection line (circle) 44.

During the fabrication of the MEMS layers (step 354 of FIG. 23),cavities are formed between the thin-film piezoelectric stack and thesemiconductor substrate at lateral positions corresponding to the PMUTs.These cavities can be formed by dry etching process after the formationof subsequent layers, such as the layers in the thin-film piezoelectricstack. In order to carry out this dry etching process, release holesshould be formed for each cavity. The release holes are holes throughwhich etchants can enter the cavity and spent etchants and etchedmaterial can exit from the cavity. The release hole for a cavity isconnected to the cavity and extends through the thin-film piezoelectricstack. It is preferable that the release holes overlap the inflectionline where the strain in the piezoelectric stack is 0. In the exampleshown in FIG. 28, there are four release holes (760, 762, 764, 766).These release holes overlap the inflection line 44. When we refer to afirst object overlapping a second object, it is not necessary that theentirety of the second object be covered by the first object. Moreover,the release holes and the first and second PMUT electrodes arepositioned relative to each other such that the release holes do notextend through the first PMUT electrode and the second PMUT electrode.

The PMUT 700 of FIG. 28 additionally includes an outer piezoelectriccapacitor. The second outer PMUT electrode (top outer PMUT electrode)724 is shown as a C-shaped ring located outside the inflection line 44.The first outer PMUT electrode (bottom outer PMUT electrode), which ishidden behind the top outer PMUT electrode, is also located outside theinflection line (circle) 44. The first outer PMUT electrode and thesecond outer PMUT electrode are positioned on opposite sides of thepiezoelectric layer to constitute an outer piezoelectric capacitor. Therelease holes and the first and second outer PMUT electrodes arepositioned relative to each other such that the release holes do notextend through the first outer PMUT electrode and the second outer PMUTelectrode.

PMUT 700 can be configured as a receiver (PMUT receiver). FIG. 29 is ablock diagram illustrating the electrical connections of PMUT 700. InFIG. 29, piezoelectric capacitor 710 (containing first PMUT electrode712 and second PMUT electrode 714) and outer piezoelectric capacitor 720(containing first outer PMUT electrode 722 and second outer PMUTelectrode 724) are connected in series 702 via a wiring trace 716. Inthe example shown, wiring trace 716 is located at 12 o'clock. The wiringtrace 716 connects the top outer PMUT electrode 724 and the top PMUTelectrode 714. Hence the wiring trace 716 does not penetrate thepiezoelectric layer. Wiring trace 718 which is connected to the topouter PMUT electrode 724 (12 o'clock) is connected to the common node.In the example shown, the wiring traces 716, 718, the top outer PMUTelectrode 724, and the top PMUT electrode 714 are contained in the samemetal layer. The outermost electrodes of the PMUT electrodes in series702 are first PMUT electrode 712 and the first outer PMUT electrode 722.These outermost electrodes are connected as differential inputs 751, 752to the amplifier circuitry 402 of the signal processing circuitry 137.The voltage signals at inputs 751, 752 are amplified by the amplifiercircuitry 402. Amplified voltage signals 440 are output from theamplifier circuitry 402 to the analog-to-digital converter (ADC) 406.Digital signals 450 are output from the ADC 406. When configured as areceiver, the PMUT 700 is sometimes referred to as a differential PMUTreceiver. PMUT 700, when configured as a receiver, can be substitutedfor any of the PMUT receivers that do not have outer electrodes. Forexample, PMUT 700, when configured as a receiver, can be substituted forany of the PMUT receivers in the arrays of FIGS. 15, 16, 17, 18, 19, 20,21, and 22.

As shown in FIG. 28, a wiring trace 711 is connected to the bottom PMUTelectrode (first PMUT electrode) 712. Wiring trace 711 extends to thesignal processing circuitry, in particular the input 751 of theamplifier circuitry 402. A wiring trace 721 is connected to the bottomouter PMUT electrode (first outer PMUT electrode) 722. Wiring trace 721extends to the signal processing circuitry, in particular the input 752of the amplifier circuitry 392. In the example shown, the wiring traces711, 721, the bottom outer PMUT electrode 722, and the bottom PMUTelectrode 712 are contained in the same metal layer. The first andsecond outer PMUT electrodes should preferably be shaped to enablewiring connections to the first and second PMUT electrodes. In theexample shown, a region of overlap of the first outer PMUT electrode 722and the second outer PMUT electrode 724 is a C-shaped ring toaccommodate the wiring trace 711 connecting the first PMUT electrode tothe signal processing circuitry. In the example shown in FIG. 28, PMUT700 include a first wiring corridor 770 and a second wiring corridor772. These wiring corridors 770, 772 traverse the inflection line 44.Wiring trace 711 is contained in a first wiring corridor 770 whichextends along the X-direction 220. The first outer PMUT electrode 722and the second PMUT electrode 724 are shaped such that they do notoverlap the first wiring corridor 770. A second wiring corridor 772,perpendicular to the first wiring corridor 770, extends along theY-direction 222. Wiring trace 716 which is connected to the second PMUTelectrode 714 is contained in the second wiring corridor 772. Therelease holes (760, 762, 764, 766) are shaped and oriented such thatthey do not overlap the first wiring corridor 770 and the second wiringcorridor 772. The release holes are shaped and oriented such that theydo not extend through any wiring that is connected to the first PMUTelectrode 712 or the second PMUT electrode 714.

FIG. 30 is a block diagram of the FMTSIC device 790, which is an exampleof a force-measuring and touch-sensing system integrated into a singleintegrated circuit device. FMTSIC device 790 includes a MEMS portion 134and an ASIC portion 796. The MEMS portion 134 includes PMUT transmitters142, PMUT receivers 144, and PMFEs 146. The ASIC portion includes thefollowing signal processing circuitry: high-voltage transceivercircuitry 382, including high-voltage drivers, amplifiers (392, 402),analog-to-digital converters (ADCs) (396, 406), and a microcontroller(MCU) 410. The high-voltage transceiver circuitry 382 is operativelycoupled to the first PMUT electrodes and the second PMUT electrodes ofthe PMUT transmitters 142. The high-voltage transceiver is configured tooutput voltage pulses of 5 V or greater, depending on the requirementsof driving the PMUT transmitters. There may be additional signalprocessing circuitry located on-chip (in the ASIC portion) and/oradditional signal processing circuitry located off-chip. Such off-chipsignal processing circuitry would be operatively coupled to the on-chipsignal processing circuitry.

MCU 410 is operatively coupled to the high-voltage transceiver circuitry382 and the ADCs (396, 406). MCU 410 generates time-varying signals thatare transmitted to the high-voltage transceiver circuitry 382. Thehigh-voltage transceiver circuitry 382 transmits high-voltage signals tothe PMUT transmitters 142 in accordance with the time-varying signalsfrom MCU 410, causing the PMUT transmitters 142 generate ultrasoundwaves. Returning ultrasound waves are incident on PMUT receivers 144.Voltage signals are generated at the PMUT receivers in response toultrasound waves incident thereon. Voltage signals output by the PMUTreceivers 144 reach amplifiers 402 (operatively coupled to PMUTreceivers 144) and get amplified by the amplifiers 402. These amplifiedvoltage signals are sent to ADC 406 (operatively coupled to theamplifiers 402) to be converted to digital signals (PMUT digital data)which can be processed by MCU 410. Similarly, voltage signals aregenerated at the PMFEs in response to a mechanical deformation. Voltagesignals output by PMFEs 146 reach amplifiers 392 (operatively coupled toPMFEs 146) and get amplified by the amplifiers 392. These amplifiedvoltage signals are sent to ADC 396 (operatively coupled to theamplifiers 392) to be converted to digital signals (PMFE digital data)which can be processed by MCU 410. Data processing and algorithms can becarried out at the MCU (410) using digital data derived from the PMUTreceivers 144 and PMFEs 146. In the example shown, the piezoelectriccapacitors constituting the PMUT receivers 144 are connected inparallel, and the piezoelectric capacitors constituting the PMUTtransmitters 142 are connected in parallel. The PMFEs 146 are groupedinto sets, with the PMFEs in each set being connected in series.

FIG. 31 is a block diagram of an example of a force-measuring andtouch-sensing system 800, a portion of which is integrated into anintegrated circuit device, namely FMTSIC device 802. The force-measuringand touch-sensing system 800 includes FMTSIC device 802 and an MCU 810.FMTSIC device 802 includes a MEMS portion 134 and an ASIC portion 806.The MEMS portion 134 includes PMUT transmitters 142, PMUT receivers 144,and PMFEs 146. The ASIC portion includes the following signal processingcircuitry: high-voltage transceiver circuitry 382, includinghigh-voltage drivers, amplifiers (392, 402), and analog-to-digitalconverters (ADCs) (396, 406). FMTSIC device 802 is similar to the FMTSICdevice 790, except that FMTSIC device 802 does not include an MCU. MCU810 can be a separate IC such as a commercially available IC. MCU 810 isoperatively coupled to the high-voltage transceiver circuitry 382 andthe ADCs (396, 406), and can operate similarly to MCU 410 of FIG. 30.

FIG. 32 is a block diagram of an example of a force-measuring andtouch-sensing system 820, which includes FMTSIC device 822 and othercircuit blocks 824. FMTSIC device 822 includes a MEMS portion 134 and anASIC portion 826. The MEMS portion 134 includes PMUT transmitters 142,PMUT receivers 144, and PMFEs 146. The ASIC portion includes thefollowing signal processing circuitry: high-voltage transceivercircuitry 382, including high-voltage drivers, and amplifiers (392,402). The configuration shown in FIG. 32 is similar to that shown inFIG. 31 except that the ADCs are moved from the FMTSIC to the othercircuit blocks. Other circuit blocks 824 include MCU 810 and ADCs (836,846).

In the example shown in FIG. 32, MCU 810 is operatively coupled to thehigh-voltage transceiver circuitry 382 and the ADCs (836, 846). Voltagesignals output by the PMUT receivers 144 reach amplifiers 402(operatively coupled to PMUT receivers 144) and get amplified by theamplifiers 402. These amplified voltage signals are sent to ADC 846(operatively coupled to the amplifiers 402) to be converted to digitalsignals (PMUT digital data) which can be processed by MCU 810. Voltagesignals output by PMFEs 146 reach amplifiers 392 (operatively coupled toPMFEs 146) and get amplified by the amplifiers 392. These amplifiedvoltage signals are sent to ADC 836 (operatively coupled to theamplifiers 392) to be converted to digital signals (PMFE digital data)which can be processed by MCU 810. Other circuit blocks 824 can beimplemented as an IC. For example, a commercially available MCU can beused as MCU 810, and ADCs in the commercially available MCU can be usedas ADCs (836, 846).

FIG. 33 is a block diagram of an example of a force-measuring andtouch-sensing system 850, which includes FMTSIC device 852 and othercircuit blocks 854. FMTSIC device 852 includes a MEMS portion 134 and anASIC portion 856. The MEMS portion 134 includes PMUT transmitters 142,PMUT receivers 144, and PMFEs 146. The ASIC portion includes thefollowing signal processing circuitry: amplifiers (392, 402). Theconfiguration shown in FIG. 33 is similar to that shown in FIG. 32except that the high-voltage transceiver circuitry are moved from theFMTSIC to the other circuit blocks. Other circuit blocks 854 include MCU810, ADCs (836, 846), and high-voltage transceiver circuitry 858. MCU810 is operatively coupled to the high-voltage transceiver circuitry858. MCU 810 generates time-varying signals that are transmitted to thehigh-voltage transceiver circuitry 858. The high-voltage transceivercircuitry 858 transmits high-voltage signals to the PMUT transmitters142.

FIG. 34 is a block diagram of an example of a force-measuring andtouch-sensing system 860, which includes FMTSIC device 862 and othercircuit blocks 864. FMTSIC device 852 includes a MEMS portion 134 and asemiconductor substrate portion 866. The MEMS portion 134 includes PMUTtransmitters 142, PMUT receivers 144, and PMFEs 146. The semiconductorsubstrate portion 866 includes electrical interconnections (wiring) 870that electrically connect the MEMS portion to the other circuit blocks864. The configuration shown in FIG. 34 is similar to that shown in FIG.33 except that the amplifiers are moved from the FMTSIC to the othercircuit blocks. Other circuit blocks 864 include MCU 810, ADCs (836,846), amplifiers (862, 872) and high-voltage transceiver circuitry 858.The high-voltage transceiver circuitry 858 transmits high-voltagesignals to the PMUT transmitters 142 via wiring 870. Voltage signalsoutput by the PMUT receivers 144 reach amplifiers 872 which areoperatively coupled (via wiring 870) to PMUT receivers 144 and getamplified by the amplifiers 872. These amplified voltage signals aresent to ADC 846 (operatively coupled to the amplifiers 872) to beconverted to digital signals (PMUT digital data) which can be processedby MCU 810. Voltage signals output by PMFEs 146 reach amplifiers 862which are operatively coupled (via wiring 870) to PMFEs 146 and getamplified by the amplifiers 862. These amplified voltage signals aresent to ADC 836 (operatively coupled to the amplifiers 862) to beconverted to digital signals (PMFE digital data) which can be processedby MCU 810. The wiring 870 on the semiconductor substrate 866 extendsfrom the semiconductor substrate 866 to the PMUTs (142, 144) and to thePMFEs (146). Other circuit blocks 854 and other off-chip signalprocessing circuitry are operatively coupled to the MEMS portion 134 viathe wiring 870 on the semiconductor substrate 866.

An example of a PMUT digital data is shown in FIG. 35, which showsgraphical plot 900 of illustrative PMUT digital data, after ADC andbefore additional processing (e.g., high-pass filtering). The graphicalplot has a horizontal axis 902 showing time t, in which 1 divisioncorresponds to 5000 ms, and a vertical axis 904 showing PMUT digitaldata (e.g., data output from ADC 406 of FIG. 30). Graphical plot 900includes sections 906, 914, 908, 916, 910, 912, 918, and 912 (orderedsequentially). Graphical plot sections 906, 908, 910, and 912 correspondto time periods during which there is nothing touching or coming intocontact with the sense region. These graphical plot sections 906, 908,910, and 912 show the baseline signal, which exhibits a drift. Plotsection 914 corresponds to repetitive pressing of a digit (e.g., afinger) on the sense region, wherein each valley 915 in the PMUT signalcorresponds to one occurrence of the digit pressing at the sense region.In the example shown, plot section 914 shows 10 repetitions of the digitpressing at the sense region. After each repetition, the digit iscompletely released (removed) from the sense region. Plot section 916also corresponds to repetitive pressing of the digit on the senseregion, but after each repetition, the digit is not completely removedfrom the sense region. During the duration of plot section 916, thedigit is in contact with the sense region. Plot section 918 correspondsto the digit touching the sense region and being held against the senseregion continuously.

FIG. 36 shows graphical plots 920, 940, and 970 of illustrative PMUTdigital data. The graphical plots have a horizontal axis 922 showingtime t, in which 1 division corresponds to 200 ms, and a vertical axis924 showing PMUT digital data. Graphical plot 920 is a graphical plot ofPMUT digital data (e.g., data output from ADC 406 of FIG. 30, beforeadditional processing) and corresponds to one occurrence of a digitpressing on the sense region and the digit being completely removed(released) from the sense region. Graphical plot 920 includes plotsections 926, 928, 930, 932, and 934 (ordered sequentially). Graphicalplot sections 926 and 934 correspond to time periods during which thereis nothing touching or coming into contact with the sense region. Thesegraphical plot sections 926 and 934 show the baseline signal. During theduration of plot section 928, the PMUT digital signal is decreasing fromthe baseline (derivative of PMUT digital signal with respect to time isnegative), approximately corresponding to the digit coming into contactwith the sense region and the digit pressing at the sense region. ThePMUT digital signal reaches a minimum at plot section 930. During theduration of plot section 932, the PMUT digital signal is increasing fromthe minimum (derivative of PMUT digital signal with respect to time ispositive), approximately corresponding to the digit being released fromthe sense region.

The PMUT digital signal (920) can undergo additional processing. In theexample shown in FIG. 36, there are two processed outputs (940, 970)from the PMUT digital signal. Plots 940, 970 show the PMUT digitalsignal 920 after passing through a high-pass filter as follows: plot 940shows the high-pass filtered output that is less than or equal to 0 andplot 970 shows the high-pass filtered output that is greater than orequal to 0. The high-pass filter processing can be carried out on theoutput from the ADCs (e.g., ADC 406 of FIG. 29). In the example shown inFIG. 30, the high-pass filtering process is carried out at the MCU 410.

Graphical plot 940 (negative-side high-pass filtered PMUT digitalsignal) includes plot sections 942, 944, 946, 948, and 950, orderedsequentially. Plot sections 942 and 950 show the baseline signal. Duringthe duration of plot section 944, the high-pass filtered PMUT digitalsignal (negative side) is decreasing from the baseline. The high-passfiltered PMUT digital signal (negative side) reaches a minimum at plotsection 946. During the duration of plot section 948, the high-passfiltered PMUT digital signal (negative side) is increasing from theminimum. Plot sections 944, 946, and 948 can correspond to an object,such as a digit, touching and pressing at the sense region. Accordingly,the negative-side high-pass filtered PMUT digital signal is sometimesreferred to as a press signal.

Graphical plot 970 (positive-side high-pass filtered PMUT digitalsignal) includes plot sections 972, 974, 976, 978, and 980, orderedsequentially. Plot sections 972 and 980 show the baseline signal. Duringthe duration of plot section 974, the high-pass filtered PMUT digitalsignal (positive side) is increasing from the baseline. The high-passfiltered PMUT digital signal (positive side) reaches a maximum at plotsection 976. During the duration of plot section 978, the high-passfiltered PMUT digital signal (positive side) is decreasing from themaximum. Plot sections 974, 976, and 978 can correspond to an object,such as a digit, being released from the sense region. Accordingly, thepositive-side high-pass filtered PMUT digital signal is sometimesreferred to as a release signal or relief signal. An end of the plotsection 948, corresponding to the negative-side high-pass filtered PMUTdigital data increasing toward the baseline, and a beginning of the plotsection 974, corresponding to the positive-side high-pass filtered PMUTdigital data increasing from the baseline, occur approximatelyconcurrently.

FIG. 37 shows a graphical plot 1010 of illustrative PMUT digital dataduring a repetitive touch event. Graphical plot 1010 has a horizontalaxis 1012 showing time t, in which 1 division corresponds to 2.0 sec,and a vertical axis 1014 showing PMUT digital data, after ADC and beforehigh-pass filtering. Graphical plot 1010 includes plot sections 1016,1018, and 1020 (ordered sequentially). Graphical plot portions 1016 and1020 correspond to time periods during which there is nothing touchingor coming into contact with the sense region. These graphical plotsections 1016 and 1020 show the baseline signal. Plot section 1018corresponds to repetitive pressing of a digit (e.g., a finger) on thesense region, wherein each valley (minimum) 1022 in the PMUT signalcorresponds to one occurrence of the digit pressing at the sense region.In the example shown, plot section 1018 shows 10 repetitions of thedigit pressing at the sense region. After each repetition, the digit iscompletely released (removed) from the sense region. As shown in FIG.37, the 10 repetitions of the digit pressing at the sense region occurduring a time period of approximately 4.1 sec. Accordingly, therepetition rate is approximately 2.4 Hz.

FIG. 38 shows a graphical plot 1030 of illustrative PMFE digital dataduring the repetitive touch event shown in FIG. 37. Graphical plot 1030has a horizontal axis 1032 showing time t, in which 1 divisioncorresponds to 2.0 sec, and a vertical axis 1034 showing PMFE digitaldata. Graphical plot 1030 includes plot sections 1036, 1038, and 1040(ordered sequentially). Graphical plot portions 1036 and 1040 correspondto time periods during which there is nothing touching or coming intocontact with the sense region. These graphical plot sections 1036 and1040 show the baseline signal. Plot section 1038 corresponds torepetitive pressing of a digit (e.g., a finger) on the sense region,analogous to plot section 1018 of FIG. 37. There is a pair of maximumPMFE digital data 1042 and a minimum PMFE digital data 1044 (occurringafter 1042) corresponding to one repetition of a digit pressing at thesense region and the digit being removed from the sense region. As thedigit presses the sense region, the PMFE(s) undergo a first deformationresulting in a first PMFE signal, and as the digit is removed from thesense region, the PMFE(s) undergo a second deformation resulting in asecond PMFE signal. In this case, the first and second deformations arein opposite directions and the first and second PMFE signals are ofopposite polarities relative to the baseline signal. As illustrated inthe example of FIG. 12, the first deformation can be a first deflectionduring which a first deflection voltage V_(d1) (corresponding to strainof a certain polarity and magnitude) is detectable. The seconddeformation can be a second deflection during which a second deflectionvoltage V_(d2) (corresponding to strain of a certain polarity andmagnitude) is detectable. As shown in FIG. 38, the 10 repetitions of thedigit pressing at the sense region occur during a time period ofapproximately 4.1 sec. Accordingly, the repetition rate is approximately2.4 Hz.

What is claimed is:
 1. A force-measuring and touch-sensing integratedcircuit device, comprising: a semiconductor substrate; wiring on thesemiconductor substrate; a thin-film piezoelectric stack overlying thesemiconductor substrate and comprising a piezoelectric layer; at leastone set of piezoelectric micromechanical force-measuring elements(PMFEs), each set comprising at least one PMFE; and an array ofpiezoelectric micromechanical ultrasonic transducers (PMUTs), each ofthe PMUTs being configured as a transmitter or a receiver; wherein thePMFEs and PMUTs are located at respective lateral positions along thethin-film piezoelectric stack, each of the PMFEs and PMUTs comprising arespective portion of the thin-film piezoelectric stack; the wiringextends from the semiconductor substrate to the PMUTs and to the PMFEs;each of the PMUTs comprises: (1) a cavity, (2) the respective portion ofthe thin-film piezoelectric stack overlying the cavity, (3) a first PMUTelectrode, and (4) a second PMUT electrode, the first PMUT electrode andthe second PMUT electrode being positioned on opposite sides of thepiezoelectric layer to constitute a piezoelectric capacitor, the PMUTsbeing coupled to the wiring, the cavity being positioned between thethin-film piezoelectric stack and the semiconductor substrate; the PMUTscomprise: (1) first transmitters (first PMUT transmitters) configured totransmit, upon application of voltage signals between the respectivefirst PMUT electrode and the respective second PMUT electrode,ultrasound signals of a first frequency F₁, in longitudinal mode(s)propagating along a normal direction approximately normal to thepiezoelectric layer and away from the cavities, and (2) first receivers(first PMUT receivers) configured to output, in response to ultrasoundsignals of the first frequency F₁ arriving along the normal direction,voltage signals between the respective first PMUT electrode and therespective second PMUT electrode (PMUT voltage signals); each of thePMFEs comprises: (1) a first PMFE electrode, (2) a second PMFEelectrode, and (3) the respective portion of the thin-film piezoelectricstack, the first PMFE electrode and the second PMFE electrode beingpositioned on opposite sides of the piezoelectric layer to constitute apiezoelectric capacitor, the PMFEs being coupled to the wiring; and eachPMFE is configured to output voltage signals between the respectivefirst PMFE electrode and the respective second PMFE electrode (PMFEvoltage signals) in accordance with a time-varying strain at therespective portion of the piezoelectric layer between the respectivefirst PMFE electrode and the respective second PMFE electrode resultingfrom a low-frequency mechanical deformation.
 2. The force-measuring andtouch-sensing integrated circuit device of claim 1, wherein therespective portions of the thin-film piezoelectric stack of the firstreceivers oscillate at the first frequency F₁ in response to ultrasoundsignals of the first frequency F₁ arriving along the normal direction.3. The force-measuring and touch-sensing integrated circuit device ofclaim 1, wherein the low-frequency mechanical deformation is induced byan excitation having a repetition rate of 100 Hz or less.
 4. Theforce-measuring and touch-sensing integrated circuit device of claim 3,wherein the repetition rate is 10 Hz or less.
 5. The force-measuring andtouch-sensing integrated circuit device of claim 1, wherein thelow-frequency mechanical deformation is induced by one or more of thefollowing: touching, pressing, bending, twisting, typing, tapping, andpinching.
 6. The force-measuring and touch-sensing integrated circuitdevice of claim 1, wherein the low-frequency mechanical deformationcomprises a deformation of an entirety of the force-measuring andtouch-sensing integrated circuit device.
 7. The force-measuring andtouch-sensing integrated circuit device of claim 1, wherein thelow-frequency mechanical deformation comprises a compression andexpansion of the piezoelectric layer along the normal direction.
 8. Theforce-measuring and touch-sensing integrated circuit device of claim 1,wherein the low-frequency mechanical deformation comprises elastic waveoscillations.
 9. The force-measuring and touch-sensing integratedcircuit device of claim 1, wherein the low-frequency mechanicaldeformation comprises expansion and/or compression of the piezoelectriclayer along a lateral direction approximately parallel to thepiezoelectric layer.
 10. The force-measuring and touch-sensingintegrated circuit device of claim 1, wherein the thin-filmpiezoelectric stack additionally comprises a mechanical layer coupled tothe piezoelectric layer.
 11. The force-measuring and touch-sensingintegrated circuit device of claim 10, wherein the mechanical layercomprises silicon, silicon oxide, silicon nitride, aluminum nitride, ora material that is included in the piezoelectric layer.
 12. Theforce-measuring and touch-sensing integrated circuit device of claim 1,wherein the piezoelectric layer comprises aluminum nitride,scandium-doped aluminum nitride, polyvinylidene fluoride (PVDF), leadzirconate titanate (PZT), K_(x)Na_(1−x)NbO₃ (KNN), quartz, zinc oxide,or lithium niobate.
 13. The force-measuring and touch-sensing integratedcircuit device of claim 1, wherein for at least one of the PMUTs, aregion of overlap of the respective first PMUT electrode and therespective second PMUT electrode is circular.
 14. The force-measuringand touch-sensing integrated circuit device of claim 1, wherein eachPMFE has lateral dimensions no greater than 2.5 mm by 2.5 mm.
 15. Theforce-measuring and touch-sensing integrated circuit device of claim 1,wherein the first receivers number less than the first transmitters. 16.The force-measuring and touch-sensing integrated circuit device of claim1, wherein more than half of the first receivers are approximatelyequidistant from a central point of the PMUT array.
 17. Theforce-measuring and touch-sensing integrated circuit device of claim 1,wherein the first frequency F₁ is in a range of 0.1 MHz to 25 MHz. 18.The force-measuring and touch-sensing integrated circuit device of claim1, wherein the semiconductor substrate additionally comprises signalprocessing circuitry coupled to the PMUTs and the PMFEs via the wiring.19. The force-measuring and touch-sensing integrated circuit device ofclaim 18, wherein the signal processing circuitry comprises ahigh-voltage transceiver circuitry configured to output voltage pulsesof 5 V or greater, the high-voltage transceiver circuitry beingconnected to the first PMUT electrodes and the second PMUT electrodes ofthe PMUTs that are configured as transmitters.
 20. The force-measuringand touch-sensing integrated circuit device of claim 18, wherein thesignal processing circuitry comprises analog-to-digital convertercircuitry for converting PMUT voltage signals to PMUT digital data andfor converting PMFE voltage signals to PMFE digital data.
 21. Theforce-measuring and touch-sensing integrated circuit device of claim 1,having lateral dimensions no greater than 10 mm by 10 mm.
 22. Theforce-measuring and touch-sensing integrated circuit device of claim 1,wherein the PMUT array has a square or rectangular outer perimeter. 23.The force-measuring and touch-sensing integrated circuit device of claim1, wherein the PMUTs additionally comprise: second transmitters (secondPMUT transmitters) configured to transmit, upon application of voltagesignals between the respective first PMUT electrode and the respectivesecond PMUT electrode, ultrasound signals of a second frequency F₂, inlongitudinal mode(s) propagating along the normal direction and awayfrom the cavities; and second receivers (second PMUT receivers)configured to output, in response to ultrasound signals of the secondfrequency F₂ arriving along the normal direction, voltage signalsbetween the respective first PMUT electrode and the respective secondPMUT electrode.
 24. The force-measuring and touch-sensing integratedcircuit device of claim 23, wherein the second receivers number lessthan the second transmitters.
 25. The force-measuring and touch-sensingintegrated circuit device of claim 23, wherein more than half of thesecond receivers are approximately equidistant from a central point ofthe PMUT array.
 26. The force-measuring and touch-sensing integratedcircuit device of claim 23, wherein the second frequency F₂ is in arange of 0.1 MHz to 25 MHz.
 27. The force-measuring and touch-sensingintegrated circuit device of claim 23, wherein the second receivers are,on average, closer than the first receivers to a central point of thePMUT array.
 28. The force-measuring and touch-sensing integrated circuitdevice of claim 1, wherein the at least one set of piezoelectricmicromechanical force-measuring elements (PMFEs) is a plurality of PMFEsets, the PMFE sets being arranged in an array.
 29. The force-measuringand touch-sensing integrated circuit device of claim 28, wherein thePMFE array is two-dimensional.
 30. The force-measuring and touch-sensingintegrated circuit device of claim 29, wherein the PMFE array has anopening in which the PMUT array is disposed.
 31. The force-measuring andtouch-sensing integrated circuit device of claim 1, wherein each PMFEset comprises a plurality of PMFEs connected in series, outermostelectrodes of the first PMFE electrodes and the second PMFE electrodesof the PMFEs in the series being connected as differential inputs to anamplifier circuitry.
 32. The force-measuring and touch-sensingintegrated circuit device of claim 31, wherein a node between twoadjacent PMFEs in the series is a common node.
 33. The force-measuringand touch-sensing integrated circuit device of claim 31, wherein eachPMFE set comprises two PMFEs connected in series and a node between thetwo PMFEs is a common node.
 34. The force-measuring and touch-sensingintegrated circuit device of claim 1, wherein: each PMUT has aninflection line in the respective portion of the thin-film piezoelectricstack; and for at least one of the PMUTs, the respective first PMUTelectrode and the respective second PMUT electrode are located insidethe respective inflection line.
 35. The force-measuring andtouch-sensing integrated circuit device of claim 34, wherein: the atleast one of the PMUTs comprises at least one release hole overlappingthe respective inflection line, extending through the respective portionof the thin-film piezoelectric stack, and connecting to the respectivecavity; and the at least one release hole does not extend through therespective first PMUT electrode and the respective second PMUTelectrode.
 36. The force-measuring and touch-sensing integrated circuitdevice of claim 35, wherein: the at least one release hole does notextend through wiring connected to the respective first PMUT electrodeand/or the respective second PMUT electrode.
 37. The force-measuring andtouch-sensing integrated circuit device of claim 34, wherein: the atleast one of the PMUTs additionally comprises a first outer PMUTelectrode and a second outer PMUT electrode, the first outer PMUTelectrode and the second PMUT electrode being positioned on oppositesides of the piezoelectric layer to constitute an outer piezoelectriccapacitor; and the first outer PMUT electrode and the second outer PMUTelectrode are located outside the respective inflection line.
 38. Theforce-measuring and touch-sensing integrated circuit device of claim 37,wherein the at least one of the PMUTs is configured as a receiver. 39.The force-measuring and touch-sensing integrated circuit device of claim37, wherein: the at least one of the PMUTs comprises at least onerelease hole overlapping the respective inflection line, extendingthrough the respective portion of the thin-film piezoelectric stack, andconnecting to the respective cavity; and the at least one release holedoes not extend through any of the following: the respective first PMUTelectrode, the respective second PMUT electrode, the respective firstouter PMUT electrode, and the respective second outer PMUT electrode.40. The force-measuring and touch-sensing integrated circuit device ofclaim 39, wherein: the at least one of the PMUTs comprises a firstwiring corridor and a second wiring corridor perpendicular to the firstwiring corridor, the first wiring corridor and the second wiringcorridor traversing the respective inflection line; wiring connected tothe respective first PMUT electrode and the respective second PMUTelectrode of the at least one of the PMUTs is contained in the firstwiring corridor and the second wiring corridor; and the at least onerelease hole does not overlap the first wiring corridor and the secondwiring corridor.
 41. The force-measuring and touch-sensing integratedcircuit device of claim 37, wherein: the at least one of the PMUTscomprises a first wiring corridor, traversing the respective inflectionline; wiring connected to the respective first PMUT electrode and/or therespective second PMUT electrode of the at least one of the PMUTs iscontained in the first wiring corridor; and the respective first outerPMUT electrode and the respective second outer PMUT electrode of the atleast one of the PMUTs do not overlap the first wiring corridor.
 42. Theforce-measuring and touch-sensing integrated circuit device of claim 41,wherein: for the at least one of the PMUTs, a region of overlap of therespective first outer PMUT electrode and the respective second outerPMUT electrode is a C-shaped ring.
 43. The force-measuring andtouch-sensing integrated circuit device of claim 37, wherein the atleast one of the PMUTs comprises the respective piezoelectric capacitorand the respective outer piezoelectric capacitor connected in series,outermost electrodes of the respective first PMUT electrode, therespective second PMUT electrode, the respective first outer PMUTelectrode, and the respective second outer PMUT electrode beingconnected as differential inputs to an amplifier circuitry.
 44. Theforce-measuring and touch-sensing integrated circuit device of claim 43,wherein a node between the respective piezoelectric capacitor and therespective outer piezoelectric capacitor in the series is a common node.45. An apparatus, comprising: a cover layer having an outer surfacewhich can be touched by a digit and an inner surface opposite the outersurface; and at least one force-measuring and touch-sensing integratedcircuit device coupled to the inner surface; wherein the at least oneforce-measuring and touch-sensing integrated circuit device comprises: asemiconductor substrate; wiring on the semiconductor substrate; athin-film piezoelectric stack overlying the semiconductor substrate andcomprising a piezoelectric layer; at least one set of piezoelectricmicromechanical force-measuring elements (PMFEs), each set comprising atleast one PMFE; and an array of piezoelectric micromechanical ultrasonictransducers (PMUTs), each of the PMUTs being configured as a transmitteror a receiver; wherein the PMFEs and PMUTs are located at respectivelateral positions along the thin-film piezoelectric stack, each of thePMFEs and PMUTs comprising a respective portion of the thin-filmpiezoelectric stack; the wiring extends from the semiconductor substrateto the PMUTs and to the PMFEs; each of the PMUTs comprises: (1) acavity, (2) the respective portion of the thin-film piezoelectric stackoverlying the cavity, (3) a first PMUT electrode, and (4) a second PMUTelectrode, the first PMUT electrode and the second PMUT electrode beingpositioned on opposite sides of the piezoelectric layer to constitute apiezoelectric capacitor, the PMUTs being coupled to the wiring, thecavity being positioned between the thin-film piezoelectric stack andthe semiconductor substrate; the PMUTs comprise: (1) first transmitters(first PMUT transmitters) configured to transmit, upon application ofvoltage signals between the respective first PMUT electrode and therespective second PMUT electrode, ultrasound signals of a firstfrequency F₁, in longitudinal mode(s) propagating along a normaldirection approximately normal to the piezoelectric layer away from thecavities and towards a sense region of the outer surface, and (2) firstreceivers (first PMUT receivers) configured to output, in response toultrasound signals of the first frequency F₁ arriving along the normaldirection, voltage signals between the respective first PMUT electrodeand the respective second PMUT electrode (PMUT voltage signals); each ofthe PMFEs comprises: (1) a first PMFE electrode, (2) a second PMFEelectrode, and (3) the respective portion of the thin-film piezoelectricstack, the first PMFE electrode and the second PMFE electrode beingpositioned on opposite sides of the piezoelectric layer to constitute apiezoelectric capacitor, the PMFEs being coupled to the wiring; and eachPMFE is configured to output voltage signals between the respectivefirst PMFE electrode and the respective second PMFE electrode (PMFEvoltage signals) in accordance with a time-varying strain at therespective portion of the piezoelectric layer between the respectivefirst PMFE electrode and the respective second PMFE electrode resultingfrom a low-frequency mechanical deformation.
 46. The apparatus of claim45, wherein the cover layer comprises a material selected from thefollowing: wood, glass, metal, plastic, leather, fabric, and ceramic.47. The apparatus of claim 45, wherein the low-frequency mechanicaldeformation is induced by an excitation having a repetition rate of 100Hz or less.
 48. The apparatus of claim 47, wherein the repetition rateis 10 Hz or less.
 49. The apparatus of claim 47, wherein the excitationoccurs at the outer surface of the cover layer.
 50. The apparatus ofclaim 47, wherein the excitation occurs at a portion of the apparatusmechanically coupled to the cover layer.
 51. The apparatus of claim 45,wherein the low-frequency mechanical deformation is induced by one ormore of the following: touching, pressing, bending, twisting, typing,tapping, and pinching.
 52. The apparatus of claim 45, wherein thelow-frequency mechanical deformation comprises a deformation of anentirety of the force-measuring and touch-sensing integrated circuitdevice.
 53. The apparatus of claim 45, wherein the low-frequencymechanical deformation comprises a compression and expansion of thepiezoelectric layer along the normal direction.
 54. The apparatus ofclaim 45, wherein the low-frequency mechanical deformation compriseselastic wave oscillations.
 55. The apparatus of claim 45, wherein thelow-frequency mechanical deformation comprises expansion and/orcompression of the piezoelectric layer along a lateral directionapproximately parallel to the piezoelectric layer.
 56. The apparatus ofclaim 45, wherein the low-frequency mechanical deformation comprises adeflection of the cover layer.
 57. The apparatus of claim 45, whereinthe semiconductor substrate additionally comprises signal processingcircuitry coupled to the PMUTs and the PMFEs via the wiring.